[libc][bazel] Create libc_release_library for release configurations. (#130694)
See PR #130327 for background and motivation. This change expands the
libc_support_library and libc_function rules to create filegroups that
allow building a collection of llvm-libc functions together, from
sources, as a part of a single cc_library that can then be used by the
downstream clients.
This change also adds an example use of this macro under
libc/test/BUILD.bazel to confirm that this macro works as expected.