lbutils: only use GNU SOURCE for syscall

and remove manual prototypes; fchmod, realpath
and so on rely on the _XOPEN_SOURCE macro.

the POSIX macro wasn't needed: _XOPEN_SOURCE
is sufficient.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/libreboot-utils/lib/rand.c

@@ -7,19 +7,21 @@
 #ifndef RAND_H
 #define RAND_H
 
-#ifdef __OpenBSD__
-#include <sys/param.h>
-#endif
-#include <sys/types.h>
-
 #if defined(USE_URANDOM) && \
     ((USE_URANDOM) > 0)
 #include <fcntl.h> /* if not arc4random: /dev/urandom */
 #elif defined(__linux__)
-#include <sys/random.h>
-#include <sys/syscall.h>
-long syscall(long number, ...);
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE 1
 #endif
+#include <sys/syscall.h>
+#include <sys/random.h>
+#endif
+
+#ifdef __OpenBSD__
+#include <sys/param.h>
+#endif
+#include <sys/types.h>
 
 #include <errno.h>
 #include <fcntl.h>