[MC][ELF] Copy top 3 bits of st_other to .symver aliases
On PowerPC64 ELFv2 ABI, the top 3 bits of st_other encode the local
entry offset. A versioned symbol alias created by .symver should copy
the bits from the source symbol.
This partly fixes PR41048. A full fix needs tracking of .set assignments
and updating st_other fields when finish() is called, see D56586.
Patch by Alfredo Dal'Ava Júnior
Differential Revision: https://reviews.llvm.org/D59436