[Sema] On Windows, silence erroneous warning when building with MSVC

Fixes what seems to be a buggy warning in MSVC:
```
[1/37] Building CXX object tools\clang\lib\Sema\CMakeFiles\obj.clangSema.dir\SemaConcept.cpp.obj
C:\git\llvm-project\clang\lib\Sema\SemaConcept.cpp(1933): warning C4101: '$S26': unreferenced local variable
```

Author: aganea

clang/lib/Sema/SemaConcept.cpp

@@ -1929,11 +1929,11 @@ auto SubsumptionChecker::find(AtomicConstraint *Ori) -> Literal {
   }
   auto It = Elems.find(ID);
   if (It == Elems.end()) {
-    It =
-        Elems
-            .insert({ID, MappedAtomicConstraint{Ori, Literal{getNewLiteralId(),
-                                                             Literal::Atomic}}})
-            .first;
+    It = Elems
+             .insert({ID,
+                      MappedAtomicConstraint{
+                          Ori, {getNewLiteralId(), Literal::Atomic}}})
+             .first;
     ReverseMap[It->second.ID.Value] = Ori;
   }
   return It->getSecond().ID;