Group signature symbol is missing when the group name is same as a section name.

[parth-07]

Group signature symbol is missing when the group name is same as a section name.

Reproducible example:

#!/usr/bin/env bash

cat >1.s <<\EOF
  .section foo,"ax",@progbits
  .globl main

main:

  .section A,"axG",@progbits,foo
EOF

cat >1.arm.s <<\EOF
  .section foo,"ax",%progbits
  .globl main

main:

  .section A,"axG",%progbits,foo
EOF

llvm-mc -triple arm -o 1.arm.o 1.arm.s -filetype obj
llvm-mc -triple riscv64 -o 1.rv64.o 1.s -filetype obj

llvm-readelf -sS 1.arm.o # .group(sh_info) is 0 and foo is missing from the symbol table
llvm-readelf -sS 1.rv64.o # .group(sh_info) is 0 and foo is missing from the symbol table

[quic-akaryaki]

I think commit 1108cf6 should be reverted instead of fixing individual regressions.
@MaskRay can you please comment on that commit? What was not optimal in the old code, so it needed to be rewritten and merged without a review? Can there be other regressions?

[MaskRay]

Looks like we don't have a test case for this weird but interesting case

% cat q.s
.section sec,"ax"
.section .foo,"axG",@progbits,sec
nop

GNU Assembler creates the STT_SECTION symbol sec and uses it as the group signature symbol.

It seems that we don't have test coverage for bool isSignature = Symbol.isSignature(); .... That motivation was that Used is almost always true, and we want to avoid a densemap call OWriter.Renames.count(&Symbol)