Merging r369184:

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r369184 | maskray | 2019-08-17 08:28:03 +0200 (Sat, 17 Aug 2019) | 9 lines

[ELF][PPC] Fix getRelExpr for R_PPC64_REL16_HI

Fixes https://github.com/ClangBuiltLinux/linux/issues/640

R_PPC64_REL16_HI was incorrectly computed as an R_ABS relocation.
rLLD368964 made it a linker failure. Change it to use R_PC to fix the
failures.

Add ppc64-reloc-rel.s for these R_PPC64_REL* tests.
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llvm-svn: 370313