Compile with std=c11 and set appropriate glibc feature test macros

might resolve #333 and #348

config.mk

@@ -37,6 +37,9 @@ scalable_icon_dir = ${icon_dir}/scalable/apps
 CFLAGS ?= -g -O2
 CFLAGS += -Wall -Wextra -pedantic
 
+# Settings for glibc >= 2.19 - may need to be adjusted for other systems
+CFLAGS += -std=c11 -D_POSIX_C_SOURCE=200809L -D_XOPEN_SOURCE=500
+
 ifeq (${curl},1)
 	CFLAGS += -DHAVE_LIBCURL
 	LDLIBS += -lcurl

src/gib_hash.c

@@ -26,6 +26,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include "gib_hash.h"
 #include "utils.h"
 #include "debug.h"
+#include <strings.h>
 
 gib_hash_node *gib_hash_node_new(char *key, void *data)
 {

src/options.c

@@ -27,6 +27,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include "feh.h"
 #include "filelist.h"
 #include "options.h"
+#include <strings.h>
 
 static void check_options(void);
 static void feh_getopt_theme(int argc, char **argv);