[llvm-branch-commits] [MC] Generate FeatureKV with compact string table (PR #206331)

[Alexis Engelke via llvm-branch-commits]

https://github.com/aengelke created https://github.com/llvm/llvm-project/pull/206331

FeatureKV is responsible for a fair amount of .data.rel.ro size and
relocations; in an all-target build, this amounts to ~139 kiB that need
to be touched on every startup. Therefore, store strings adjacent to the
SubtargetFeatureKV in memory and reference the strings via relative
offsets to avoid dynamic relocations.