[Clang][CodeGen][AIX] Map __builtin_frexpl, __builtin_ldexpl, and __builtin_modfl...

[Clang][CodeGen][AIX] Map __builtin_frexpl, __builtin_ldexpl, and __builtin_modfl to 'double' version lib calls in 64-bit 'long double' mode

Summary:
AIX library functions frexpl(), ldexpl(), and modfl() are for 128-bit IBM long double, i.e. __ibm128. Other *l() functions, e.g., acosl(), are for 64-bit long double. The AIX Clang compiler currently maps builtin functions __builtin_frexpl(), __builtin_ldexpl(), and __builtin_modfl() to frexpl(), ldexpl(), and modfl() in 64-bit long double mode which results in seg-faults or incorrect return values. This patch changes to map __builtin_frexpl(), __builtin_ldexpl(), and __builtin_modfl() to double version lib functions frexp(), ldexp() and modf() in 64-bit long double mode.

Reviewed by: hubert.reinterpretcast, daltenty

Differential Revision: https://reviews.llvm.org/D137986