Add base relative relocation record that can be used for the following case (OpenCL example):

static __global int Var = 0; 
__global int* Ptr[] = {&Var};
...

In this case Var is a non premptable symbol and so its address can be used as the value of Ptr, with a base relative relocation that will add the delta between the ELF address and the actual load address. Such relocations do not require a symbol.

This also fixes LLD which was incorrectly generating a PCREL64 for this case.

Differential Revision: https://reviews.llvm.org/D38910

llvm-svn: 315936