config.h: define _GNU_SOURCE

Otherwise we don't get goodies like asprintf, and 64-bit offsets.  Should
be a harmless-define on non-glibc systems.

config.h

+/* Generated by CCAN configurator */
 #ifndef CCAN_CONFIG_H
 #define CCAN_CONFIG_H
-/* Generated by CCAN configurator */
+#define _GNU_SOURCE /* Always use GNU extensions. */
 #define CCAN_COMPILER "cc"
 #define CCAN_CFLAGS "-g -Wall -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations"
 

tools/configurator/configurator.c

@@ -337,9 +337,10 @@ int main(int argc, char *argv[])
 	unlink(INPUT_FILE);
 
 	cmd[strlen(cmd) - strlen(" -o " OUTPUT_FILE " " INPUT_FILE)] = '\0';
-	printf("#ifndef CCAN_CONFIG_H\n"
-	       "#define CCAN_CONFIG_H\n"
-	       "/* Generated by CCAN configurator */\n");
+	printf("/* Generated by CCAN configurator */\n"
+	       "#ifndef CCAN_CONFIG_H\n"
+	       "#define CCAN_CONFIG_H\n");
+	printf("#define _GNU_SOURCE /* Always use GNU extensions. */\n");
 	printf("#define CCAN_COMPILER \"%s\"\n", argv[1]);
 	printf("#define CCAN_CFLAGS \"%s\"\n\n", cmd + strlen(argv[1]) + 1);
 	for (i = 0; i < sizeof(tests)/sizeof(tests[0]); i++)