[ELF] Add R_ARM_RELATIVE to relocations that can be applied to GotSection

    
When compiling -fpie and linking with the --pie option the R_ARM_GOTBREL
relocation to D is resolved by writing the value of D into the .got slot
and emitting an R_ARM_RELATIVE relocation for it.
    
This changes adds the R_ARM_RELATIVE relocation to the switch in
relocateOne() so we can process the GotSection relocation to write the
value of the variable as well as emitting the dynamic relocation.

Differential revision: https://reviews.llvm.org/D27678

llvm-svn: 289527