[mips] Revert fixes for PR32020.

The fix introduces segfaults and clobbers the value to be stored when
the atomic sequence loops.

Revert "[Target/MIPS] Kill dead code, no functional change intended."

This reverts commit r296153.

Revert "Recommit "[mips] Fix atomic compare and swap at O0.""

This reverts commit r296134.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297380 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed