GNU3 demangler: fix __int128 literal type and .eh extension spacing

- Fix DemanglePrimaryExpression 'n' case: type is __int128 (signed),
  not __uint128 — matches the Itanium ABI spec for type code 'n'
- Fix dot-extension appending (.eh, .eh_frame, etc.): add space before
  the human-readable extension name to avoid "fooexception handler"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: plafosse

demangler/gnu3/demangle_gnu3.cpp

@@ -1078,7 +1078,7 @@ string DemangleGNU3::DemanglePrimaryExpression()
 	case 'l': out = DemangleNumberAsString() + "l"; break;  //long
 	case 'x': out = DemangleNumberAsString() + "ll"; break;  //long long
 	case 's': out = "(short)" + DemangleNumberAsString(); break; //short
-	case 'n': out = "(__uint128)" + DemangleNumberAsString() + "ull"; break;  //__int128
+	case 'n': out = "(__int128)" + DemangleNumberAsString(); break;  //__int128
 	case 'i': out = DemangleNumberAsString(); break;       // int
 	case 'm': out = DemangleNumberAsString() + "ul"; break;  //unsigned long
 	case 't': out = "(unsigned short)" + DemangleNumberAsString(); break; //unsigned short
@@ -2762,7 +2762,7 @@ DemangledTypeNode DemangleGNU3::DemangleSymbol(QualifiedName& varName)
 
 			// On the off chance some invalid mangled string is passed in.
 			if (varName.size() > 0)
-				varName.back() += ext;
+				varName.back() += " " + ext;
 			break;
 		}