Ensure that the __clzsi2 symbol is present

e310e36 solved static linking and the MinGW-w64 builds but included a
workaround for Rust 1.34 and 1.35 that didn't work for Rust 1.36.

The main problem with Rust 1.34 and 1.35 is that it included its own version
of the `__clzsi2` intrinsic instead of the C version. This caused duplicate
symbols during linking and required a workaround by removing the duplicated
symbol, see:
rust-lang/rust#58277

Fortunately, this is solved within rustc 1.36, see:
rust-lang/compiler-builtins@752e35a

The workaround, however, did not ensure that `__clzsi2` intrinsic is only
removed when it is duplicated (it could also remove the optimized C version).

This commit ensures that the `__clzsi2` intrinsic is present only once. Note
that the entire workaround can be removed when the minimum Rust version is
bumped to 1.36.

Closes: https://gitlab.gnome.org/GNOME/librsvg/issues/485

Makefile.am

@@ -136,11 +136,11 @@ cargo_verbose_ = $(cargo_verbose_$(AM_DEFAULT_VERBOSITY))
 cargo_verbose_0 =
 cargo_verbose_1 = --verbose
 
-RUST_LIB=@abs_top_builddir@/.libs/librsvg_internals.a
-CARGO_TARGET_DIR=@abs_top_builddir@/target
-
 LIBRSVG_BUILD_DIR=@abs_top_builddir@
-LIBRSVG_TARGET_DIR=@abs_top_builddir@/target/@RUST_TARGET_SUBDIR@
+CARGO_TARGET_DIR=$(LIBRSVG_BUILD_DIR)/target
+LIBRSVG_TARGET_DIR=$(CARGO_TARGET_DIR)/$(RUST_TARGET_SUBDIR)
+
+RUST_LIB=$(LIBRSVG_BUILD_DIR)/.libs/librsvg_internals.a
 
 check-local:
 	cd $(srcdir) && \
@@ -177,7 +177,9 @@ librsvg_internals.la: $(librsvg_internals_la_SOURCES)
 	LIBRSVG_BUILD_DIR=$(LIBRSVG_BUILD_DIR)					\
 	LIBRSVG_TARGET_DIR=$(LIBRSVG_TARGET_DIR)					\
 	$(CARGO) --locked build $(CARGO_VERBOSE) $(CARGO_TARGET_ARGS) $(CARGO_RELEASE_ARGS) --features "c-library" \
-	&& $(AR) d $(RUST_LIB) clzsi2.o # HACK: https://github.com/rust-lang/rust/issues/58277
+	&& if [[ $$($(NM) -g $(RUST_LIB) | grep "T __clzsi2" -c) -gt 1 ]] ; then \
+		$(AR) d $(RUST_LIB) clzsi2.o;					\
+	fi
 
 librsvg_@RSVG_API_MAJOR_VERSION@_la_CPPFLAGS = \
 	-I$(top_srcdir) 			\

configure.ac

@@ -109,6 +109,7 @@ AS_IF(test x$RUSTC = xno,
     AC_MSG_ERROR([rustc is required.  Please install the Rust toolchain from https://www.rust-lang.org/])
 )
 AC_CHECK_PROGS(AR, ar)
+AC_CHECK_PROGS(NM, nm)
 
 dnl Minimum version of rustc that we support
 dnl If you change this, please update COMPILING.md

rsvg_internals/build.rs

@@ -7,7 +7,7 @@ use std::path::Path;
 use std::os::unix::fs::symlink;
 
 #[cfg(all(windows, not(target_env = "msvc")))]
-use std::os::windows::fs::symlink_file;
+use std::os::windows::fs::symlink_file as symlink;
 
 #[cfg(not(target_env = "msvc"))]
 use std::fs;