Remove _GLIBCXX_CONCEPT_CHECKS debug define

This debug feature does not support any C++11 features.
It breaks for example the compilation of vector<unique_ptr>.

The upstream issue is:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57011

configure.ac

@@ -203,7 +203,6 @@ if test "$DEBUG" != "no"; then
 		# But they cause crashes on cygwin while loading modules
 		AC_DEFINE([_GLIBCXX_DEBUG], [1], [Enable extra debugging checks in libstdc++])
 		AC_DEFINE([_GLIBCXX_DEBUG_PEDANTIC], [1], [Enable extra debugging checks in libstdc++])
-		AC_DEFINE([_GLIBCXX_CONCEPT_CHECKS], [1], [Enable extra debugging checks in libstdc++])
 	fi
 else
 	if test "x$OPTIMIZE" = "xyes"; then