Switch master patches over to GCC's next development cycle.
Update target-ver-syms for MinGW

We do not have/need libm on MiGW
Trivial build fixes for MinGW/druntime
Implement GDC-vararg handling in std.format for MinGW
GDC inline ASM fixes for MinGW
Extern variable _CRT_MT is __gshared
MinGW64 does not provide __imp symbols for InterlockedExchange
Thread, Fiber & GC support for MinGW
Fix main function for MinGW
Add mingw README
Fix TypeInfo name mangling for MinGW
Merge pull request #77 from jpf91/windows

Initial MinGW support
Merge commit '7353ff361384673d34acfc5891a3de5c2b375148' into gdc-4.9

Conflicts:
	gcc.version
Merge branch 'master' into gdc-4.9