[Sema] Avoid repeated hash lookups (NFC) (#112071)

Author: kazutakahirata

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -4057,11 +4057,10 @@ TemplateDeductionResult Sema::FinishTemplateArgumentDeduction(
   // keep track of these diagnostics. They'll be emitted if this specialization
   // is actually used.
   if (Info.diag_begin() != Info.diag_end()) {
-    SuppressedDiagnosticsMap::iterator
-      Pos = SuppressedDiagnostics.find(Specialization->getCanonicalDecl());
-    if (Pos == SuppressedDiagnostics.end())
-        SuppressedDiagnostics[Specialization->getCanonicalDecl()]
-          .append(Info.diag_begin(), Info.diag_end());
+    auto [Pos, Inserted] =
+        SuppressedDiagnostics.try_emplace(Specialization->getCanonicalDecl());
+    if (Inserted)
+      Pos->second.append(Info.diag_begin(), Info.diag_end());
   }
 
   return TemplateDeductionResult::Success;