[NFC][LTO] Move isPreservedName out of IRSymtab into LTO's Symbol as isLibcall (#177046)
This resolves the FIXME in IRSymtab and cleans up the semantics of the
IRSymtab. The list of preserved symbols really shouldn't be seen as a
property of the IR symbol table, since it's an LTO-specific concern, and
it's very tenuous to claim that this information is actually present in
the bitcode file to be exposed through its symbol table.
Instead, this PR moves this logic into LTO's view of the symbol, which
allows consumers to determine preserved-ness themselves. This was broken
out of #164916; this prevents that PR from introducing a circular
dependency, but it still seems like an independently good idea by virtue
of the above.
llvm-project
567fe2bb - [NFC][LTO] Move isPreservedName out of IRSymtab into LTO's Symbol as isLibcall (#177046)
