[x86] Clean up the x86 builtin specs to reflect r217310 in LLVM which
made the 8-bit masks actually 8-bit arguments to these intrinsics.

These builtins are a mess. Many were missing the I qualifier which
I added where obviously correct. Most aren't tested, but I've updated
the relevant tests. I've tried to catch all the things that should
become 'c' in this round.

It's also frustrating because the set of these is really ad-hoc and
doesn't really map that cleanly to the set supported by either GCC or
LLVM. Oh well...