[CIR][Lowering] Erase op through rewriter instead of directly (llvm#853)

Directly erasing the op causes a use after free later on, presumably
because the lowering framework isn't aware of the op being deleted. This
fixes `clang/test/CIR/CodeGen/pointer-arith-ext.c` with ASAN.

Author: smeenai

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

@@ -608,7 +608,7 @@ class CIRPtrStrideOpLowering
                 index.getLoc(), index.getType(),
                 mlir::IntegerAttr::get(index.getType(), 0)),
             index);
-        sub->erase();
+        rewriter.eraseOp(sub);
       }
     }