Allow setting command prefix for precompile execution

This change adds some flexibility to how precompile execution files
are executed by PackageCompiler to generate precompile statements.

In some cases, for example when one wants to use precompile statements
generated from a script that uses a package that uses MPI and requires
that the Julia process is started via `mpiexec` or similar,
one currently has to execute the script manually and use Julia's
`--trace-compile` option to generate precompile statements and pass
them manually to PackageCompiler afterwards.

The new `precompile_execution_prefix` keyword argument introduced by
this commit allows one to skip manual generation of precompile
statements in such cases by passing the necessary prefix to
PackageCompiler.

src/PackageCompiler.jl

@@ -278,11 +278,12 @@ function ensurecompiled(project, packages, sysimage)
     return
 end
 
-function run_precompilation_script(project::String, sysimg::String, precompile_file::Union{String, Nothing}, precompile_dir::String)
+function run_precompilation_script(project::String, sysimg::String, precompile_prefix::Cmd,
+                                   precompile_file::Union{String, Nothing}, precompile_dir::String)
     tracefile, io = mktemp(precompile_dir; cleanup=false)
     close(io)
     arg = precompile_file === nothing ? `-e ''` : `$precompile_file`
-    cmd = `$(get_julia_cmd()) --sysimage=$(sysimg) --compile=all --trace-compile=$tracefile $arg`
+    cmd = `$precompile_prefix $(get_julia_cmd()) --sysimage=$(sysimg) --compile=all --trace-compile=$tracefile $arg`
     # --project is not propagated well with Distributed, so use environment
     splitter = Sys.iswindows() ? ';' : ':'
     @debug "run_precompilation_script: running $cmd" JULIA_LOAD_PATH = "$project$(splitter)@stdlib"
@@ -299,6 +300,7 @@ function create_sysimg_object_file(object_file::String,
                             project::String,
                             base_sysimage::String,
                             precompile_execution_file::Vector{String},
+                            precompile_execution_prefix::Cmd,
                             precompile_statements_file::Vector{String},
                             cpu_target::String,
                             script::Union{Nothing, String},
@@ -326,7 +328,8 @@ function create_sysimg_object_file(object_file::String,
     @debug "running precompilation execution script..."
     precompile_dir = mktempdir(; prefix="jl_packagecompiler_", cleanup=false)
     for file in (isempty(precompile_execution_file) ? (nothing,) : precompile_execution_file)
-        tracefile = run_precompilation_script(project, base_sysimage, file, precompile_dir)
+        tracefile = run_precompilation_script(project, base_sysimage, precompile_execution_prefix,
+                                              file, precompile_dir)
         push!(precompile_files, tracefile)
     end
     append!(precompile_files, abspath.(precompile_statements_file))
@@ -487,11 +490,16 @@ compiler (can also include extra arguments to the compiler, like `-g`).
 
 - `sysimage_build_args::Cmd`: A set of command line options that is used in the Julia process building the sysimage,
   for example `-O1 --check-bounds=yes`.
+
+- `precompile_execution_prefix::Cmd`: A set of commands and command line options that will be
+  prefixed to the call to Julia when executing files specified by `precompile_execution_file`,
+  for example `srun`.
 """
 function create_sysimage(packages::Union{Nothing, Symbol, Vector{String}, Vector{Symbol}}=nothing;
                          sysimage_path::String,
                          project::String=dirname(active_project()),
                          precompile_execution_file::Union{String, Vector{String}}=String[],
+                         precompile_execution_prefix::Cmd=``,
                          precompile_statements_file::Union{String, Vector{String}}=String[],
                          incremental::Bool=true,
                          filter_stdlibs::Bool=false,
@@ -599,6 +607,7 @@ function create_sysimage(packages::Union{Nothing, Symbol, Vector{String}, Vector
                             project,
                             base_sysimage,
                             precompile_execution_file,
+                            precompile_execution_prefix,
                             precompile_statements_file,
                             cpu_target,
                             script,
@@ -789,11 +798,16 @@ compiler (can also include extra arguments to the compiler, like `-g`).
   for example `-O1 --check-bounds=yes`.
 
 - `script::String`: Path to a file that gets executed in the `--output-o` process.
+
+- `precompile_execution_prefix::Cmd`: A set of commands and command line options that will be
+  prefixed to the call to Julia when executing files specified by `precompile_execution_file`,
+  for example `srun`.
 """
 function create_app(package_dir::String,
                     app_dir::String;
                     executables::Union{Nothing, Vector{Pair{String, String}}}=nothing,
                     precompile_execution_file::Union{String, Vector{String}}=String[],
+                    precompile_execution_prefix::Cmd=``,
                     precompile_statements_file::Union{String, Vector{String}}=String[],
                     incremental::Bool=false,
                     filter_stdlibs::Bool=false,
@@ -848,6 +862,7 @@ function create_app(package_dir::String,
                     incremental,
                     filter_stdlibs,
                     precompile_execution_file,
+                    precompile_execution_prefix,
                     precompile_statements_file,
                     cpu_target,
                     sysimage_build_args,
@@ -986,11 +1001,16 @@ compiler (can also include extra arguments to the compiler, like `-g`).
 
 - `sysimage_build_args::Cmd`: A set of command line options that is used in the Julia process building the sysimage,
   for example `-O1 --check-bounds=yes`.
+
+- `precompile_execution_prefix::Cmd`: A set of commands and command line options that will be
+  prefixed to the call to Julia when executing files specified by `precompile_execution_file`,
+  for example `srun`.
 """
 function create_library(package_or_project::String,
                         dest_dir::String;
                         lib_name=nothing,
                         precompile_execution_file::Union{String, Vector{String}}=String[],
+                        precompile_execution_prefix::Cmd=``,
                         precompile_statements_file::Union{String, Vector{String}}=String[],
                         incremental::Bool=false,
                         filter_stdlibs::Bool=false,
@@ -1051,7 +1071,7 @@ function create_library(package_or_project::String,
     compat_file = get_library_filename(lib_name; version, compat_level)
     soname = (Sys.isunix() && !Sys.isapple()) ? compat_file : nothing
 
-    create_sysimage_workaround(ctx, sysimg_path, precompile_execution_file,
+    create_sysimage_workaround(ctx, sysimg_path, precompile_execution_file, precompile_execution_prefix,
         precompile_statements_file, incremental, filter_stdlibs, cpu_target;
         sysimage_build_args, include_transitive_dependencies, julia_init_c_file,
         julia_init_h_file, version, soname, script)
@@ -1108,6 +1128,7 @@ function create_sysimage_workaround(
                     ctx,
                     sysimage_path::String,
                     precompile_execution_file::Union{String, Vector{String}},
+                    precompile_execution_prefix::Cmd,
                     precompile_statements_file::Union{String, Vector{String}},
                     incremental::Bool,
                     filter_stdlibs::Bool,
@@ -1143,6 +1164,7 @@ function create_sysimage_workaround(
                     incremental=true,
                     script=script,
                     precompile_execution_file,
+                    precompile_execution_prefix,
                     precompile_statements_file,
                     cpu_target,
                     base_sysimage,