Use -std=gnu++11 instead of -std=c++11 due to gcc extensions

config.lib

@@ -1242,6 +1242,8 @@ make_compiler_cflags() {
 	eval eval "ldflags=\\\$$4"
 	eval eval "features=\\\$$5"
 
+	cppstd="-std=c++11"
+
 	if [ `echo "$version_line" | cut -d' ' -f1` = "icc" ]; then
 		# Enable some things only for certain ICC versions
 		cc_version=`$1 -dumpversion | cut -c 1-4 | sed s@\\\.@@g`
@@ -1407,6 +1409,7 @@ make_compiler_cflags() {
 		flags="$flags -Wwrite-strings -Wpointer-arith"
 		flags="$flags -W -Wno-unused-parameter -Wredundant-decls"
 		flags="$flags -Wformat=2 -Wformat-security"
+		cppstd="-std=gnu++11"
 
 		if [ $enable_assert -eq 0 ]; then
 			# Do not warn about unused variables when building without asserts
@@ -1497,7 +1500,7 @@ make_compiler_cflags() {
 	fi
 
 	eval "$2=\"$flags\""
-	eval "$3=\"$cxxflags\""
+	eval "$3=\"$cxxflags $cppstd\""
 	eval "$4=\"$ldflags\""
 	eval "$5=\"$features\""
 }
@@ -1533,8 +1536,6 @@ make_cflags_and_ldflags() {
 
 	CFLAGS="$CFLAGS -D$os"
 	CFLAGS_BUILD="$CFLAGS_BUILD -D$os"
-	CXXFLAGS="$CXXFLAGS -std=c++11"
-	CXXFLAGS_BUILD="$CXXFLAGS_BUILD -std=c++11"
 
 	if [ "$enable_debug" = "0" ]; then
 		# No debug, add default stuff