Our "struct tm" doesn't have a tm_gmtoff field; work around this
(including a patch to to avoid an unused variable error)

--- gnucash-5.11/CMakeLists.txt.~1~	Sat Mar 29 21:03:36 2025
+++ gnucash-5.11/CMakeLists.txt	Wed Apr 30 14:16:11 2025
@@ -808,7 +808,7 @@
 set (HAVE_SETENV 1)
 set (HAVE_STPCPY 1)
 set (HAVE_STRPTIME 1)
-set (HAVE_STRUCT_TM_GMTOFF 1)
+set (HAVE_STRUCT_TM_GMTOFF 0)
 set (HAVE_TIMEGM 1)
 set (HAVE_TOWUPPER 1)
 set (GNC_PLATFORM_POSIX 1)
--- gnucash-5.11/common/base-typemaps.i.~1~	Mon Nov 11 18:02:44 2024
+++ gnucash-5.11/common/base-typemaps.i	Wed Apr 30 14:28:17 2025
@@ -95,6 +95,8 @@
     SCM zone = SCM_SIMPLE_VECTOR_REF(tm, 10);
     tzone = SCM_UNBNDP(zone) ? NULL : scm_to_locale_string(zone);
     t.tm_zone = tzone;
+%#else
+    (void)tzone;
 %#endif
     $1 = &t;
  }
--- gnucash-5.11/libgnucash/engine/test/test-gnc-date.c.~1~	Mon Nov 11 18:02:45 2024
+++ gnucash-5.11/libgnucash/engine/test/test-gnc-date.c	Thu May  1 12:18:36 2025
@@ -1151,7 +1155,7 @@
     time64 now = gnc_time(NULL);
     gchar buff[MAX_DATE_LENGTH];
     struct tm tm = { 0, 0, 0, 0, 0, 0, 0, 0, 0
-#ifndef G_OS_WIN32
+#ifdef HAVE_STRUCT_TM_GMTOFF
         , 0, 0
 #endif
     };