[PowerPC][FP128] Fix the incorrect signature for math library call

The runtime library has two family library implementation for ppc_fp128 and fp128.
For IBM Long double(ppc_fp128), it is suffixed with 'l', i.e(sqrtl). For
IEEE Long double(fp128), it is suffixed with "ieee128" or "f128".
We miss to map several libcall for IEEE Long double.

Reviewed By: qiucf

Differential Revision: https://reviews.llvm.org/D91675