RuntimeLibcalls: Add definitions for vector math functions (#167026)

This is mostly the output of a vibe coded script running on
VecFuncs.def, with a lot of manual cleanups and fixing where the
vibes were off. This is not yet wired up to anything (except for the
handful of calls which are already manually enabled). In the future
the SystemLibrary mechanism needs to be generalized to allow plugging
these sets in based on the flag.

One annoying piece is there are some name conflicts across the
libraries. Some of the libmvec functions have name collisions with some 
sleef functions. I solved this by just adding a prefix to the libmvec functions. 
It would probably be a good idea to add a prefix to every group. It gets ugly,
particularly since some of the sleef functions started to use a Sleef_
prefix, but mostly do not.

Author: arsenm