Fix building with GCC 12

[marxin]

Summary

Fixes: https://bugs.llvm.org/show_bug.cgi?id=52380

[jwakely]

I think the C++ standard says this code should work, despite being stupid. But the const should be there anyway, because it doesn't modify anything.

[foad]

Looks fine to me if it works. See also D112897.

[jwakely]

N.B. the libstdc++ regression that caused this to fail has been fixed now.

llvm/lib/Target/AMDGPU/SILoadStoreOptimizer.cpp

if (MergeList.size() <= 1) {
       I = MergeableInsts.erase(I);
       continue;
     }
 
     // Sort the lists by offsets, this way mergeable instructions will be
     // adjacent to each other in the list, which will make it easier to find
     // matches.
     MergeList.sort(
-        [] (const CombineInfo &A, CombineInfo &B) {
+        [] (const CombineInfo &A, const CombineInfo &B) {
           return A.Offset < B.Offset;
         });
     ++I;
   }
 
   return std::make_pair(BlockI, Modified);
 }