Completely rewrite ELFObjectWriter::RecordRelocation.

I started trying to fix a small issue, but this code has seen a small fix too
many.

The old code was fairly convoluted. Some of the issues it had:

* It failed to check if a symbol difference was in the some section when
  converting a relocation to pcrel.
* It failed to check if the relocation was already pcrel.
* The pcrel value computation was wrong in some cases (relocation-pc.s)
* It was missing quiet a few cases where it should not convert symbol
  relocations to section relocations, leaving the backends to patch it up.
* It would not propagate the fact that it had changed a relocation to pcrel,
  requiring a quiet nasty work around in ARM.
* It was missing comments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205076 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp

@@ -116,7 +116,8 @@ MCObjectWriter *MipsAsmBackend::createObjectWriter(raw_ostream &OS) const {
 /// data fragment, at the offset specified by the fixup and following the
 /// fixup kind as appropriate.
 void MipsAsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
-                                unsigned DataSize, uint64_t Value) const {
+                                unsigned DataSize, uint64_t Value,
+                                bool IsPCRel) const {
   MCFixupKind Kind = Fixup.getKind();
   Value = adjustFixupValue(Fixup, Value);