[LLVM-521] LLD and taking the address of an ifunc

Went through the possible combinations (pic, pie, non-pic, exec, shared,...) found one relocation that gcc uses that clang doesn't, hence mc and LLD don't support. Raised upstream pr. Also found that clang's code-sequence for -fpie doesn't seem to guarantee ifunc pointer equivalence when linking -fpie (non-got generating sequence used when ifunc is in same translation unit). Will need some further investigation to confirm.

[LLVM-499] Support for linking the linux kernel Committed -pic-veneer support and associated overflow fix, now merged to 8.0 branch.

Other: - Started work on Fosdem presentation on LLD performance. Studying ld.bfd and ld.gold source code to look for structural differences between them and LLD. - Submitted presentation for next Linaro Connect - Review for comdat group and unused section elimination. - On buildbot duty.