[ELF][I386] .got.plt entries for i386 should use VA of ifunc resolver

The i386 glibc ld.so expects the .got.slot entry that is relocated by a 
R_386_IRELATIVE relocation to point directly at the ifunc resolver and
not the address of the PLT entry + 6 (thus entering the lazy resolver).
This is also the case for ARM and I suspect it is because these use REL
relocations and can't use the addend field to store the address of the
ifunc resolver. If the lazy resolver is used we get an error message
stating that only R_386_JUMP_SLOT is supported.

As ARM and i386 share the same code, I've removed the ARM specific test
and added a writeIgotPlt() function that by default calls writeGotPlt().
ARM and i386 override this to write the address of the ifunc resolver.

Differential Revision: https://reviews.llvm.org/D27581

llvm-svn: 289198