[CodeGen] Avoid repeated hash lookup (NFC) (#108735)

Author: kazutakahirata

clang/lib/CodeGen/CGOpenMPRuntime.cpp

@@ -7815,12 +7815,7 @@ class MappableExprsHandler {
             const Expr *VarRef = nullptr, bool ForDeviceAddr = false) {
           if (SkipVarSet.contains(D))
             return;
-          auto It = Info.find(D);
-          if (It == Info.end())
-            It = Info
-                     .insert(std::make_pair(
-                         D, SmallVector<SmallVector<MapInfo, 8>, 4>(Total)))
-                     .first;
+          auto It = Info.try_emplace(D, Total).first;
           It->second[Kind].emplace_back(
               L, MapType, MapModifiers, MotionModifiers, ReturnDevicePointer,
               IsImplicit, Mapper, VarRef, ForDeviceAddr);