start on windows jit support

  - Replacement for in-memory JIT mmap,mprotect,munmap.

  - dylib feature disabled (for now, but could be done
    with LoadLibrary/GetProcAddress)

  - Mostly share impl with __x86_64__, but with enter
    and exit updated for the MS ABI.

I "rediscovered" along the way that r12 has the same low three
bits as rsp, and that means the assembler needs to handle it
specially in at least one place it's not today.  No big deal;
we can easily avoid using r12.  GP registers are all statically
allocated.  Left a warning and a TODO.

Still need to investigate 17 GMs that are triggering asserts.

Change-Id: I0f543b0efab968e805e89dcf1f068eac1cafea38
Commit-Queue: Mike Klein <>
Reviewed-by: Herb Derby <>
3 files changed