[Mips] Sort R_MIPS_LO16 / R_MIPS_HI16 / R_MIPS_GOT16 before finding
pairs and calculate AHL addend.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@204606 91177308-0d34-0410-b5e6-96231b3b80d8