RuntimeLibcalls: Introduce LibcallLibrary schema (#217592)
Currently the set of system libraries calls is flat and
disorganized. Begin organizing this per-provider library.
The goal is to organize groups of functions by named sets,
corresponding to the underlying library which will be linked.
A LibcallLibrary is a named runtime library whose impls are made
available as a unit; its members use the same dag vocabulary as
LibcallImpls. The emitter emits one setAvailableLibFuncs_<name>
per distinct library name, merging same-named libraries under their
per-variant availability predicates. isLibraryAvailable()
is added as a stub for a future dispatch driver. No target
defines a LibcallLibrary, so generated output is mostly unchanged
(there are some incidental enum reorderings).
Reorganizing all of the library functions require a good bit more
infrastructure to be practical, but this is a minimally functional
piece to start the review.
Co-authored-by: Claude (Claude-Opus-4.8) <noreply@anthropic.com>
