Host endianness was not correctly detected, as exposed by:

[937/6175] Building C object Source/ThirdParty/xdgmime/CMakeFiles/xdgmime.dir/src/xdgmimemagic.c.o
/z/ws/oi-userland-gnucash/components/library/webkitgtk/webkitgtk-2.42.5/Source/ThirdParty/xdgmime/src/xdgmimemagic.c: In function '_xdg_mime_magic_parse_magic_line':
/z/ws/oi-userland-gnucash/components/library/webkitgtk/webkitgtk-2.42.5/Source/ThirdParty/xdgmime/src/xdgmimemagic.c:489:5: warning: "LITTLE_ENDIAN" is not defined, evaluates to 0 [-Wundef]
  489 | #if LITTLE_ENDIAN
      |     ^~~~~~~~~~~~~
/z/ws/oi-userland-gnucash/components/library/webkitgtk/webkitgtk-2.42.5/Source/ThirdParty/xdgmime/src/xdgmimemagic.c:482:15: warning: unused variable 'i' [-Wunused-variable]
  482 |           int i;
      |               ^


--- webkitgtk-2.48.1/Source/ThirdParty/xdgmime/src/xdgmimemagic.c.orig
+++ webkitgtk-2.48.1/Source/ThirdParty/xdgmime/src/xdgmimemagic.c
@@ -30,6 +30,7 @@
 #endif
 
 #include <assert.h>
+#include <endian.h>
 #include "xdgmimemagic.h"
 #include "xdgmimeint.h"
 #include <stdio.h>
@@ -488,7 +489,7 @@
 	      return XDG_MIME_MAGIC_ERROR;
 	    }
 	  /* FIXME: need to get this defined in a <config.h> style file */
-#if LITTLE_ENDIAN
+#if BYTE_ORDER == LITTLE_ENDIAN
 	  for (i = 0; i < matchlet->value_length; i = i + matchlet->word_size)
 	    {
 	      if (matchlet->word_size == 2)