[lld] Merge equivalent symbols found during ICF (#134342)
Fixes a correctness issue for AArch64 when ADRP and LDR instructions are
outlined in separate sections and sections are fed to ICF for
deduplication.
See test case (based on
https://github.com/llvm/llvm-project/issues/129122) for details. All
rodata.* sections are folded into a single section with ICF. This leads
to all f2_* function sections getting folded into one (as their
relocation target symbols g* belong to .rodata.g* sections that have
already been folded into one). Since relocations still refer original g*
symbols, we end up creating duplicate GOT entry for all such symbols.
This PR addresses that by tracking such folded symbols and create one
GOT entry for all such symbols.
Fixes https://github.com/llvm/llvm-project/issues/129122
Co-authored by: @jyknight
