[libc] Add long double flavors of the floating point manipulation functions.

Specifically: copysignl, frexpl, logbl and modfl have been added.

Reviewers: asteinhauser

Differential Revision: https://reviews.llvm.org/D82357

GitOrigin-RevId: a00fb593b4ed3e7e6313b9afcd3657d4650e509f
19 files changed