Modify llvm-gsymutil to ignore invalid file indexes (#71431)

DWARF produced by LTO and BOLT can sometimes be broken where file
indexes are beyond the end of the line table's file list in the
prologue. This patch allows llvm-gsymutil to convert this DWARF without
crashing, and emits errors when:

line table contains entries with an invalid file index (line entry will
be removed) inline functions that have invalid DW_AT_call_file file
indexes when there are no line table entries for a function and we fall
back to making a single line table entry from the functions
DW_AT_decl_file/DW_AT_decl_line attributes, we make sure the
DW_AT_decl_file attribute is valid before emitting it.