Symtab is first filled with the data from the bitcode file, and all
undefined symbols except TLS ones are `STT_NOTYPE`. Since auth key for a
signed GOT entry depends on the symbol type being `STT_FUNC` or not, we
need to update the symtab after the bitcode is compiled to an ELF object
and update symbol types for function symbols. This patch implements the
described behavior.
8fdebff69d