[mips] Implement generation of relocations "chains" used by N32 ABI

In case of using a "nested" relocation expressions like this
`%hi(%neg(%gp_rel()))`, N32 ABI requires generation of three consecutive
relocations. That differs from the N64 ABI case where all relocations
are packed into the single relocation record.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313879 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed