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

llvm-svn: 233205