Fix potential Out-of-order Evaluation in DebugInfo

In DebugTypeInfoRemoval, DenseMap Replacements's assignment's rvalue is a recursive function that may access Replacements itself. Since C++17 such an "right to left" order cannot get guaranteed.
This change is to separate 1 line into 2.

Author: NaiveWang

llvm/lib/IR/DebugInfo.cpp

@@ -798,7 +798,8 @@ class DebugTypeInfoRemoval {
 
       return getReplacementMDNode(N);
     };
-    Replacements[N] = doRemap(N);
+    auto value = doRemap(N);
+    Replacements[N] = value;
   }
 
   /// Do the remapping traversal.