Use non-serialized Win32 Heap API with DMC

Create an alternative implementstion of rmem.c that uses Win32 Heap API.

Use it instead of rmem.c when buidling with DMC (win32.mak).

This alone brings 
dmd -unittest -c std\algorithm.d

from ~13.3 sec to ~8.0 sec

Could serve as an interim solution, the alternative is to tweak DMC's allocator..