[jitlink][ELF] Add zero-fill blocks for symbols in section SHN_COMMON

Symbols with special section index SHN_COMMON (0xfff2) haven't been handled so far and caused an invalid section error.

This is a more or less straightforward use of the code commented out at the end of the function. I checked with the ELF spec, that the symbol value gives the alignment.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D89795