No longer generate calls to *_finite

According to Joseph Myers, a libm maintainer

> They were only ever an ABI (selected by use of -ffinite-math-only or
> options implying it, which resulted in the headers using "asm" to redirect
> calls to some libm functions), not an API. The change means that ABI has
> turned into compat symbols (only available for existing binaries, not for
> anything newly linked, not included in static libm at all, not included in
> shared libm for future glibc ports such as RV32), so, yes, in any case
> where tools generate direct calls to those functions (rather than just
> following the "asm" annotations on function declarations in the headers),
> they need to stop doing so.

As a consequence, we should no longer assume these symbols are available on the
target system.

Still keep the TargetLibraryInfo for constant folding.

Differential Revision: https://reviews.llvm.org/D74712