[Power9] Add remaining __flaot128 builtin support for FMA round to odd

Implement this as it is done on GCC:

__float128 a, b, c, d;
a = __builtin_fmaf128_round_to_odd (b, c, d);         // generates xsmaddqpo
a = __builtin_fmaf128_round_to_odd (b, c, -d);        // generates xsmsubqpo
a = - __builtin_fmaf128_round_to_odd (b, c, d);       // generates xsnmaddqpo
a = - __builtin_fmaf128_round_to_odd (b, c, -d);      // generates xsnmsubpqp

Differential Revision: https://reviews.llvm.org/D48218

llvm-svn: 336754