d3d12: Fixes compile error with mingw/gcc-x64 when static linkage to runtime library
Closes #6968 Signed-off-by: Yonggang Luo <luoyonggang@gmail.com> Suggested-by: Jesse Natalie <jenatali@microsoft.com> Reviewed-by: Jesse Natalie <jenatali@microsoft.com> Tested-by: Prodea Alexandru-Liviu <liviuprodea@yahoo.com> Part-of: <mesa/mesa!17889> (cherry picked from commit b6fb2da6)