[llvm-readobj] [ARMWinEH] Try to resolve label symbols into regular ones

Unwind info generated by MSVC tends to have relocations pointing at
static "label" symbols like "$LN4" instead of regular ones based on
the actual function's name. Try to resolve such symbols to a non-label
symbol if possible (ideally to an external symbol), to improve
the readability.

Differential Revision: https://reviews.llvm.org/D101567