Fix many clang errors in UIUC code

- because uiuc_warning_error always called exit(-1), it can be marked
  no return, so Clang realises that when it’s used in the ‘else’
  side of a parsing test, uninitialised variables in the enclosing
  call site are safe.

(Requires Simgear update to define SG_NO_RETURN helper)

src/FDM/UIUCModel/uiuc_warnings_errors.cpp

@@ -118,6 +118,9 @@ void uiuc_warnings_errors(int errorCode, std::string line)
       exit(-1);
       break;
     }
+
+    cerr << "UIUC UNKNOWN ERROR" << endl;
+    exit(-1);
 }
 
 // end uiuc_warnings_errors.cpp

src/FDM/UIUCModel/uiuc_warnings_errors.h

@@ -6,6 +6,6 @@
 #include <string>
 #include <cstdlib>
 
-void uiuc_warnings_errors(int errorCode, std::string line);
+SG_NO_RETURN void uiuc_warnings_errors(int errorCode, std::string line);
 
 #endif  //_WARNINGS_ERRORS_H_