Use <startup.h> in __libc_init_secure

Since __libc_init_secure is called before ARCH_SETUP_TLS, it must use
"int $0x80" for system calls in i386 static PIE.  Add startup_getuid,
startup_geteuid, startup_getgid and startup_getegid to <startup.h>.
Update __libc_init_secure to use them.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/generic/startup.h

@@ -19,5 +19,31 @@
 /* Targets should override this file if the default definitions below
    will not work correctly very early before TLS is initialized.  */
 
+#include <unistd.h>
+
 /* Use macro instead of inline function to avoid including <stdio.h>.  */
 #define _startup_fatal(message) __libc_fatal ((message))
+
+static inline uid_t
+startup_getuid (void)
+{
+  return __getuid ();
+}
+
+static inline uid_t
+startup_geteuid (void)
+{
+  return __geteuid ();
+}
+
+static inline gid_t
+startup_getgid (void)
+{
+  return __getgid ();
+}
+
+static inline gid_t
+startup_getegid (void)
+{
+  return __getegid ();
+}