gtksourceviewmm2: require C++11

gnome/gtksourceviewmm2/Portfile

@@ -15,9 +15,8 @@ long_description \
 
 maintainers     {devans @dbevans} openmaintainer
 categories      gnome
-platforms       darwin
  
-homepage        http://projects.gnome.org/gtksourceviewmm/
+homepage        https://projects.gnome.org/gtksourceviewmm
 master_sites    gnome:sources/${gname}/${branch}/
 
 distname        ${gname}-${version}
@@ -34,6 +33,12 @@ depends_build   port:pkgconfig
 depends_lib     port:gtkmm \
                 port:gtksourceview2
 
+compiler.cxx_standard \
+                2011
+# Clang fails to build it without an explicit flag:
+configure.cxxflags-append \
+                -std=c++11
+
 livecheck.type  gnome
 livecheck.name  ${gname}
 livecheck.regex "LATEST-IS-(${port_ver_major}\\.\\d*\[02468\](?:\\.\\d+)*)"