Bug 1220470

Building efitools with GCC 14 fails here:
https://build.opensuse.org/package/live_build_log/openSUSE:Factory:Staging:Gcc7/efitools/standard/x86_64

Due to:

sign-efi-sig-list.c: In function ‘main’:
sign-efi-sig-list.c:166:17: error: implicit declaration of function ‘strptime’; did you mean ‘strftime’? [-Wimplicit-function-declaration]
  166 |                 strptime(timestampstr, "%Y-%m-%d %H:%M:%S", &tms);
      |                 ^~~~~~~~
      |                 strftime

flash-var.c: In function ‘main’:
flash-var.c:109:17: error: implicit declaration of function ‘strptime’; did you mean ‘strftime’? [-Wimplicit-function-declaration]
  109 |                 strptime(timestampstr, "%Y-%m-%d %H:%M:%S", &tms);
      |                 ^~~~~~~~
      |                 strftime


Builds with:

Index: efitools.spec_dir/efitools-1.9.2/sign-efi-sig-list.c
===================================================================
--- efitools.spec_dir.orig/efitools-1.9.2/sign-efi-sig-list.c
+++ efitools.spec_dir/efitools-1.9.2/sign-efi-sig-list.c
@@ -3,6 +3,7 @@
  *
  * see COPYING file
  */
+#define _XOPEN_SOURCE
 #include <stdint.h>
 #define __STDC_VERSION__ 199901L
 #include <efi.h>
Index: efitools.spec_dir/efitools-1.9.2/flash-var.c
===================================================================
--- efitools.spec_dir.orig/efitools-1.9.2/flash-var.c
+++ efitools.spec_dir/efitools-1.9.2/flash-var.c
@@ -1,3 +1,4 @@
+#define _XOPEN_SOURCE
 #include <stdlib.h>
 #include <stdint.h>
 #include <sys/types.h>