Fix llama runner cmake for android (#2673)

Summary:
Pull Request resolved: #2673

This diff fixes:
1. Make sure we buidl static variant lib for ANDROID
2. Compile libexecutorch as whole-archive to not drop prim ops registration
3. gflags and executorch's *-config.cmake wasn't found so explicitly set the
directory path.
4. Add log as dep for android as cpuinfo depends on it.
ghstack-source-id: 220378206
exported-using-ghexport

Pre-existing lint failures
bypass-github-export-checks
bypass-github-pytorch-ci-checks

Reviewed By: digantdesai, mcr229

Differential Revision: D55344017

fbshipit-source-id: 6c2158db60d22c8441584ea5a9fbad1087aa621c

examples/models/llama2/CMakeLists.txt

@@ -20,6 +20,10 @@ project(llama_runner)
 
 option(EXECUTORCH_BUILD_OPTIMIZED "Build the optimized kernels" OFF)
 
+if(NOT PYTHON_EXECUTABLE)
+  set(PYTHON_EXECUTABLE python3)
+endif()
+
 set(EXECUTORCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/../../..)
 set(TORCH_ROOT ${EXECUTORCH_ROOT}/third-party/pytorch)
 
@@ -34,13 +38,21 @@ if(NOT CMAKE_CXX_STANDARD)
   # Can't set to 11 due to executor_runner.cpp make_unique
 endif()
 
+if(CMAKE_TOOLCHAIN_FILE MATCHES ".*(iOS|ios\.toolchain)\.cmake$")
+  set(CMAKE_TOOLCHAIN_IOS ON)
+else()
+  set(CMAKE_TOOLCHAIN_IOS OFF)
+endif()
+
 set(_common_compile_options -Wno-deprecated-declarations -fPIC)
 
 # Let files say "include <executorch/path/to/header.h>".
 set(_common_include_directories ${EXECUTORCH_ROOT}/..)
 
-find_package(gflags REQUIRED PATHS
-             ${CMAKE_CURRENT_BINARY_DIR}/../../../third-party)
+# For some reason android build is not able to find where gflags is
+# and hence cannot find corresponding .cmake file
+set(gflags_DIR ${CMAKE_CURRENT_BINARY_DIR}/../../../third-party/gflags)
+find_package(gflags REQUIRED)
 
 #
 # llama_main: test binary to run llama, with tokenizer and sampler integrated
@@ -52,7 +64,12 @@ if(CMAKE_BUILD_TYPE EQUAL "RELEASE")
 endif()
 
 # find `executorch` libraries
+# Same as for gflags
+set(executorch_DIR ${CMAKE_CURRENT_BINARY_DIR}/../../../lib/cmake/ExecuTorch)
 find_package(executorch CONFIG REQUIRED)
+if(CMAKE_TOOLCHAIN_IOS OR ANDROID)
+  target_link_options_shared_lib(executorch)
+endif()
 
 # custom ops library
 add_subdirectory(custom_ops)
@@ -91,6 +108,12 @@ if(TARGET vulkan_backend)
   target_link_options_shared_lib(vulkan_backend)
 endif()
 
+# This one is needed for cpuinfo where it uses android
+# specific log lib
+if(ANDROID)
+  list(APPEND link_libraries log)
+endif()
+
 target_compile_options(llama_main PUBLIC ${_common_compile_options}
   -DET_USE_THREADPOOL)
 target_link_libraries(llama_main PUBLIC ${link_libraries})

examples/models/llama2/runner/CMakeLists.txt

@@ -39,7 +39,7 @@ list(TRANSFORM _llama_runner__srcs PREPEND "${EXECUTORCH_ROOT}/")
 target_include_directories(extension_module
                            INTERFACE ${_common_include_directories})
 
-if(CMAKE_TOOLCHAIN_IOS OR CMAKE_TOOLCHAIN_ANDROID OR APPLE)
+if(CMAKE_TOOLCHAIN_IOS OR ANDROID OR APPLE)
   # Building a share library on iOS requires code signing
   # On Android we see duplicated registration when using shared lib
   add_library(llama_runner STATIC ${_llama_runner__srcs})