[ELF2] - Implemented R_X86_64_PLT32 relocation.

There is sometimes no need to generate relocation via PLT. 
Example - when symbol is not undefined and we are not creating shared library. Then we can create relative relocation instead of referencing and creating PLT records.

Differential Revision: http://reviews.llvm.org/D13835

llvm-svn: 250584