[Preprocessor/Modules] Separate the macro directives kinds into their own MacroDirective's subclasses.

For each macro directive (define, undefine, visibility) have a separate object that gets chained
to the macro directive history. This has several benefits:

-No need to mutate a MacroDirective when there is a undefine/visibility directive. Stuff like
 PPMutationListener become unnecessary.
-No need to keep extra source locations for the undef/visibility locations for the define directive object
 (which is the majority of the directives)
-Much easier to hide/unhide a section in the macro directive history.
-Easier to track the effects of the directives across different submodules.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@178037 91177308-0d34-0410-b5e6-96231b3b80d8
Add PRFCHW intrinsic support

- Add head 'prfchwintrin.h' to define '_m_prefetchw' which is mapped to
  LLVM/clang prefetch builtin
- Add option '-mprfchw' to enable PRFCHW feature and pre-define '__PRFCHW__'
  macro



git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@178041 91177308-0d34-0410-b5e6-96231b3b80d8