util/nvramtool: fix building on OpenBSD

OpenBSD's gcc 4.2.1 doesn't know about _Noreturn

Change-Id: Ie9e1885c483941d3d0ce8c8948af53f1ef8bb5db
Signed-off-by: Evgeny Zinoviev <me@ch1p.io>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38348
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Idwer Vollering <vidwer@gmail.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/nvramtool/common.c

@@ -56,7 +56,7 @@ int get_line_from_file(FILE * f, char line[], int line_buf_size)
  *
  * We ran out of memory.  Print an error message and die.
  ****************************************************************************/
-_Noreturn void out_of_memory(void)
+noreturn void out_of_memory(void)
 {
 	fprintf(stderr, "%s: Out of memory.\n", prog_name);
 	exit(1);