selftests/nolibc: drop include guards around standard headers

Nolibc now provides all the headers required by nolibc-test.c.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20250515-nolibc-sys-v1-9-74f82eea3b59@weissschuh.net
Acked-by: Willy Tarreau <w@1wt.eu>

tools/testing/selftests/nolibc/nolibc-test-linkage.c

@@ -2,9 +2,7 @@
 
 #include "nolibc-test-linkage.h"
 
-#ifndef NOLIBC
 #include <errno.h>
-#endif
 
 void *linkage_test_errno_addr(void)
 {

tools/testing/selftests/nolibc/nolibc-test.c

@@ -9,12 +9,9 @@
  *   $(CC) -nostdlib -I/path/to/nolibc/sysroot  => _NOLIBC_* guards are present
  *   $(CC) with default libc                    => NOLIBC* never defined
  */
-#ifndef NOLIBC
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#ifndef _NOLIBC_STDIO_H
-/* standard libcs need more includes */
 #include <sys/auxv.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
@@ -43,8 +40,6 @@
 #include <unistd.h>
 #include <limits.h>
 #include <ctype.h>
-#endif
-#endif
 
 #pragma GCC diagnostic ignored "-Wmissing-prototypes"