Add Hardware Transactional Memory (HTM) Support

Add Hardware Transactional Memory (HTM) Support

This patch adds Hardware Transaction Memory (HTM) support supported by ISA 2.07
(POWER8). The intrinsic support is based on GCC one [1], with both 'PowerPC HTM
Low Level Built-in Functions' and 'PowerPC HTM High Level Inline Functions'
implemented.

Along with builtins a new driver switch is added to enable/disable HTM
instruction support (-mhtm) and a header with common definitions (mostly to
parse the TFHAR register value). The HTM switch also sets a preprocessor builtin
HTM.

The HTM usage requires a recently newer kernel with PPC HTM enabled. Tested on
powerpc64 and powerpc64le.

This is send along a llvm patch to enabled the builtins and option switch.

[1]
https://gcc.gnu.org/onlinedocs/gcc/PowerPC-Hardware-Transactional-Memory-Built-in-Functions.html

Phabricator Review: http://reviews.llvm.org/D8248

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@233205 91177308-0d34-0410-b5e6-96231b3b80d8