Fix link error for windows release builds.

https://ci.chromium.org/ui/p/gn/builders/try.shadow/win/b8674262571164089329/overview
Change-Id: I7759b7f77491ac7195a6aa8bc4405d496a6a6964
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/24960
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: Matt Stark <msta@google.com>

build/gen.py

diff --git a/build/gen.py b/build/gen.py
index bf4e5db..0c5630f 100755
--- a/build/gen.py
+++ b/build/gen.py
@@ -409,7 +409,7 @@
                                       os.path.dirname(path)))),
         '  includes = %s' % ' '.join(
             ['-I' + escape_path_ninja(dirname) for dirname in include_dirs]),
-        '  cflags = %s' % ' '.join(cflags),
+        '  cflags = %s' % ' '.join(settings.get('cflags', cflags)),
     ])
 
   for library, settings in static_libraries.items():
@@ -757,7 +757,13 @@
           'sources': [
               'src/gn/string_atom.cc',
               'src/gn/ffi/intern_string.cc',
-          ]
+          ],
+          # Strip /GL from string_atom.
+          # The Rust types crate references intern_string via a raw extern "C"
+          # declaration. If compiled with /GL, the MSVC linker discards this
+          # symbol during the LTCG phase because it has no references from
+          # C++ /GL objects, causing LNK2001 link errors in Rust test binaries.
+          'cflags': [f for f in cflags if f != '/GL']
       },
       'gn_lib': {
           'sources': [

build/run_cargo.py

diff --git a/build/run_cargo.py b/build/run_cargo.py
index a5ba52a..2faadff 100755
--- a/build/run_cargo.py
+++ b/build/run_cargo.py
@@ -203,6 +203,14 @@
   out_path = Path(out_path_str)
   cargo_out_dir = Path(cargo_out_dir_str)
 
+  if sys.platform == 'win32':
+    # Strip /GL from Cargo C++ dependencies (like the cxx crate).
+    # Rust code compiles to standard COFF objects. If C++ FFI shims generated by Cargo
+    # are compiled with /GL, the MSVC linker (running with /LTCG) fails to match the
+    # standard COFF Rust references to these C++ symbols during the LTCG phase,
+    # causing it to discard the shims as unused and leading to LNK2001 link errors.
+    cxxflags = cxxflags.replace('/GL', '')
+
   os.environ['CXX'] = cxx
   os.environ['CXXFLAGS'] = cxxflags
   # Since Ninja runs commands from the build output directory, CWD is the