[llvm] [Mips] Fix $gp was restored when used as global register variable (PR #201778)

[Matt Arsenault via llvm-commits]

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@@ -89,20 +97,23 @@ MipsRegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
                                      : CSR_Interrupt_32_SaveList;
   }
 
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arsenm wrote:

Not all of these ABIs are tested 

https://github.com/llvm/llvm-project/pull/201778