Allow C++11 "explicit constexpr"

CHANGES.current

@@ -5,6 +5,10 @@ See the RELEASENOTES file for a summary of changes in each release.
 Version 3.0.4 (in progress)
 ===========================
 
+2015-01-08: olly
+	    Allow C++11 "explicit constexpr".  Fixes github issue#284 reported
+	    by Paweł Tomulik.
+
 2015-01-08: olly
 	    When reporting an error for a construct which hasn't been
 	    terminated when the end of the file is reached, report it at the

Examples/test-suite/cpp11_constexpr.i

@@ -18,6 +18,8 @@ struct ConstExpressions {
   static const int LLL = 300;
   constexpr int MMM() { return 400; }
   constexpr const int NNN() { return 500; }
+  // Regression test for https://github.com/swig/swig/issues/284 :
+  explicit constexpr ConstExpressions(int) { }
 };
 %}
 

Source/CParse/parser.y

@@ -4680,6 +4680,7 @@ storage_class  : EXTERN { $$ = "extern"; }
                | FRIEND { $$ = "friend"; }
                | EXPLICIT { $$ = "explicit"; }
                | CONSTEXPR { $$ = "constexpr"; }
+               | EXPLICIT CONSTEXPR { $$ = "explicit constexpr"; }
                | STATIC CONSTEXPR { $$ = "static constexpr"; }
                | THREAD_LOCAL { $$ = "thread_local"; }
                | THREAD_LOCAL STATIC { $$ = "static thread_local"; }