[llvm-mc] - Produce R_X86_64_PLT32 for "call/jmp foo".

For instructions like call foo and jmp foo patch changes
relocation produced from R_X86_64_PC32 to R_X86_64_PLT32.
Relocation can be used as a marker for 32-bit PC-relative branches.
Linker will reduce PLT32 relocation to PC32 if function is defined locally.

Differential revision: https://reviews.llvm.org/D43383

llvm-svn: 325569