XXX unbreak (at least!) the following ports (wait until upstream copes):
devel/libvmime
editors/libreoffice
games/0ad/base
games/openra
lang/php/7.4
www/webkitgtk4
x11/gnustep/base
x11/qt5/qtwebengine
x11/qt5/qtwebkit

Index: source/common/unicode/umachine.h
--- source/common/unicode/umachine.h.orig
+++ source/common/unicode/umachine.h
@@ -258,6 +258,7 @@ typedef int8_t UBool;
  *
  * @internal ICU 68
  */
+#define U_DEFINE_FALSE_AND_TRUE 1
 #ifdef U_DEFINE_FALSE_AND_TRUE
     // Use the predefined value.
 #else