RuntimeLibcalls: Use explicit types for F80, F128 and PPCF128 libcalls
LDbl only makes sense for encoding the long double libm functions. Other
functions have need of the specific type. Separately, LDbl brokenly assumes
double instead of checking the module's long double format. Some functions
are inappropriately using a specific type instead of LDbl. I'll fix both
of these issues separately.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>