This patch adds support for the `libmvec` vector library on AArch64
targets. Currently, all `libmvec` functions in GLIBC version 2.40 are
supported. The full list of math functions enabled can be found
[here](96abd59bf2/sysdeps/aarch64/fpu/Versions)
(up to GLIBC 2.40).
Previously, `libmvec` was only supported on x86_64 targets. Attempts to
use it on AArch64 resulted in the following error from Clang:
`unsupported option 'libmvec' for target 'aarch64'`.