[ByteCode] Avoid repeated hash lookups (NFC) (#126379)

Author: kazutakahirata

clang/lib/AST/ByteCode/Program.cpp

@@ -18,14 +18,12 @@ using namespace clang;
 using namespace clang::interp;
 
 unsigned Program::getOrCreateNativePointer(const void *Ptr) {
-  auto It = NativePointerIndices.find(Ptr);
-  if (It != NativePointerIndices.end())
-    return It->second;
+  auto [It, Inserted] =
+      NativePointerIndices.try_emplace(Ptr, NativePointers.size());
+  if (Inserted)
+    NativePointers.push_back(Ptr);
 
-  unsigned Idx = NativePointers.size();
-  NativePointers.push_back(Ptr);
-  NativePointerIndices[Ptr] = Idx;
-  return Idx;
+  return It->second;
 }
 
 const void *Program::getNativePointer(unsigned Idx) {