RuntimeLibcalls: Add definitions for vector math functions

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