[PATCH] Allow _MSC_EXTENSIONS macro on non-Windows targets

[Yunzhong Gao]

  Hi David,

  To summarize our discussion:
  1) the _MSC_EXTENSION macro indicates compatibility with "cl.exe /Ze"
  2) Some of the behaviors of "cl.exe /Ze" is implemented for Windows target, but
  not under control of -fms-extensions
  3) Turning on -fms-extensions for non-Windows target will get the MS keywords,
  but not the ABI-specific behaviors expected of "cl.exe /Ze"

  Since it is not feasible to define _MSC_EXTENSIONS for -fms-extensions, is
  it acceptable to define a new macro, which the users can use to guard their
  MS keywords? For example, _MS_EXTENSIONS.

  - Gao

http://llvm-reviews.chandlerc.com/D3034