[MCParser] Avoid repeated hash lookups (NFC) (#110204)

Author: kazutakahirata

llvm/lib/MC/MCParser/MasmParser.cpp

@@ -479,9 +479,7 @@ class MasmParser : public MCAsmParser {
   void addDirectiveHandler(StringRef Directive,
                            ExtensionDirectiveHandler Handler) override {
     ExtensionDirectiveMap[Directive] = Handler;
-    if (!DirectiveKindMap.contains(Directive)) {
-      DirectiveKindMap[Directive] = DK_HANDLER_DIRECTIVE;
-    }
+    DirectiveKindMap.try_emplace(Directive, DK_HANDLER_DIRECTIVE);
   }
 
   void addAliasForDirective(StringRef Directive, StringRef Alias) override {