Don't pass `-Wl,--as-needed` when linking on Mingw

[Naveen M K]

Hi,

While building gn on mingw+clang (using clang64 environment from MSYS2),
I get an error while linking

[199/282] LINK gn.exe
FAILED: gn.exe
g++ -O3 -fdata-sections -ffunction-sections -Wl,--gc-sections
-Wl,-strip-all -Wl,--as-needed -static-libstdc++ -o gn.exe
-Wl,--start-group src/gn/gn_main.obj base.lib gn_lib.lib -Wl,--end-group
-ladvapi32 -ldbghelp -lkernel32 -lole32 -lshell32 -luser32 -luserenv
-lversion -lwinmm -lws2_32 -lshlwapi
lld: error: unknown argument: --as-needed
g++: error: linker command failed with exit code 1 (use -v to see
invocation)

I generated the ninja file with

python build/gen.py --out-path=out/${CARCH} --platform=mingw

I don't think `-Wl,--as-needed` argument is meaningful is for windows
binaries and lld doesn't support it. Note: in above log `g++` is aliased
to `clang++`.

It would be better if something like this was changed in `build/gen.py`,

diff --git a/build/gen.py b/build/gen.py
index 922bf46f..edcc0353 100755
--- a/build/gen.py
+++ b/build/gen.py
@@ -375,7 +375,8 @@ def WriteGNNinja(path, platform, host, options):
])

if platform.is_linux() or platform.is_mingw() or platform.is_msys():
- ldflags.append('-Wl,--as-needed')
+ if not platform.is_mingw():
+ ldflags.append('-Wl,--as-needed')

if not options.no_static_libstdcpp:
ldflags.append('-static-libstdc++')

Thanks,
Naveen M K