[llvm-readobj] Allow syms from all sections to match stack size entries

Prior to this change, for non-relocatable objects llvm-readobj would
assume that all symbols that corresponded to a stack size section's
entries were in the section specified by the section's sh_link field.
In the presence of an output section description combining
SHF_LINK_ORDER sections linking different output sections, this cannot
be respected, since linker script section patterns are "by name" by
nature. Consequently, the sh_link value would not be correct for all
section entries.

This patch changes llvm-readobj to ignore the section of symbols in a
non-relocatable object.

Fixes https://bugs.llvm.org/show_bug.cgi?id=45228.

Reviewed by: grimar, MaskRay

Differential Revision: https://reviews.llvm.org/D76425