mingw64-* regression: LTO builds fail

[Christian Franke]

After upgrading to recent mingw64 toolchain, builds with link time 
optimizer fail during linking.

Testcase:

$ cat true.c
int main() { return 0; }

$ cygcheck -f /usr/bin/i686-w64-mingw32-gcc
mingw64-i686-gcc-core-4.9.2-1

$ cygcheck -f /usr/bin/i686-w64-mingw32-ld
mingw64-i686-binutils-2.25.0.1.23f238d-1

$ i686-w64-mingw32-gcc -flto true.c
/tmp/ccukCXyi.ltrans0.ltrans.o:ccukCXyi.ltrans0.o:(.text+0x0): multiple 
definition of `main'
/usr/i686-w64-mingw32/sys-root/mingw/lib/../lib/libmingw32.a(lib32_libmingw32_a-crt0_c.o):/usr/src/debug/mingw64-i686-runtime-4.0.2-1/crt/crt0_c.c:17: 
first defined here
/usr/i686-w64-mingw32/sys-root/mingw/lib/../lib/libmingw32.a(lib32_libmingw32_a-crt0_c.o): 
In function `main':
/usr/src/debug/mingw64-i686-runtime-4.0.2-1/crt/crt0_c.c:18: undefined 
reference to `WinMain@16'
collect2: error: ld returned 1 exit status

Same with x86_64 mingw.


Downgrading the mingw64 binutils package helps:

$ cygcheck -f /usr/bin/i686-w64-mingw32-gcc
mingw64-i686-gcc-core-4.9.2-1

$ cygcheck -f /usr/bin/i686-w64-mingw32-ld
mingw64-i686-binutils-2.24.0.3.85cf705-1

$ i686-w64-mingw32-gcc -flto true.c


May or may not be an upstream issue. The current mingw64 toolchain on 
Debian jessie (gcc 4.9.1-19+14.3, binutils 2.25-5+5.2) works as expected.

Christian


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