[LLD][ELF] - ICF: Check we do not fold sections which relocations reffering to...

[LLD][ELF] - ICF: Check we do not fold sections which relocations reffering to absolute symbols with a different values.

This adds a test for the following uncovered piece of code:
https://github.com/llvm-mirror/lld/blob/master/ELF/ICF.cpp#L263

Without that lines we would crash.

llvm-svn: 338379