The main motivation for this change is to avoid ambiguity because
mapping symbol names may not be unique across a binary and do not allow uniquely
identifying target address. So that mapping symbols used as branch target
labels make llvm-objdump output less readable.
Another point is that mapping symbols sometimes appear in
non-allocatable sections, like debug info sections which make objdump
output even more confusing.
For example, a small AArch64 executable may contain plenty of `$d[.*]`
symbols and none of them would be useful as a label for resolving
a branch or a memory operand target address:
```
0000000000000254 l .note.ABI-tag 0000000000000000 $d
00000000000008d4 l .eh_frame 0000000000000000 $d
0000000000000868 l .rodata 0000000000000000 $d
0000000000011028 l .data 0000000000000000 $d
0000000000010db8 l .fini_array 0000000000000000 $d
0000000000010db0 l .init_array 0000000000000000 $d
00000000000008e8 l .eh_frame 0000000000000000 $d
0000000000011034 l .bss 0000000000000000 $d
```
Note that GNU objdump doesn't use mapping symbols as branch target
labels for all targets that support such symbols (ARM, AArch64, CSKY).
Differential Revision: https://reviews.llvm.org/D139131
4e958b4d7c