[ELF] - Implemented -z combrelocs/nocombreloc.
This is the option which sorts relocs to optimize dynamic linker performance.
-z combelocs is the default in gold, also it ignores -z nocombreloc,
this patch do the same.
Patch sorts relocations by symbols only and do not create any
DT_REL[A]COUNT entries. That is different with what gold/bfd do.
Differential revision: http://reviews.llvm.org/D19528