Link libgcc and libstdc++ statically on mingw build of llvm

This is required to eliminate llvm-config.exe dependency on
libgcc_s_sjlj-1.dll and libstdc++-6.dll on mingw cross build.
It should fix mclinker build on windows.

Change-Id: Ibdc56218d91a588f1b7826b117707672e3ba0934
Signed-off-by: Pavel Chupin <pavel.v.chupin@intel.com>
1 file changed