[X86] Expose the various _rot intrinsics on non-MS platforms

_rotl, _rotwl and _lrotl (and their right-shift counterparts) are official x86
intrinsics, and should be supported regardless of environment. This is in contrast
to _rotl8, _rotl16, and _rotl64 which are MS-specific.

Note that the MS documentation for _lrotl is different from the Intel 
documentation. Intel explicitly documents it as a 64-bit rotate, while for MS,
since sizeof(unsigned long) for MSVC is always 4, a 32-bit rotate is implied.

Differential Revision: http://reviews.llvm.org/D12271

llvm-svn: 245923