also avoid unnecessary escaping of single quotes inside double quoted
strings (depends on a master branch commit that will be merged into this
branch in a future commit)
This replaces the previous target cpu features tool, taking advantage of
llvm-tblgen --dump-json instead of trying to use python to parse the .td
files.
This is an initial version that has the basics working, including a
simple feature override system, as well as multi-threaded processing.
Follow-up commits will do clean ups to make the diff of the newly generated
source files against previous versions be as desired.
