Unbreak with icu4c >=68.1

--- src/definitions.h.orig	Sun Dec 13 12:38:01 2020
+++ src/definitions.h	Mon Dec 14 08:22:25 2020
@@ -42,14 +42,7 @@
 #endif
 
 /*==== Misc definitions ====*/
-/* Define a bool type if not already defined (C++ and C99 do)*/
-#if !(defined(__cplusplus) || (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L))
-/*@-incondefs@*/
-typedef enum {false, true} bool;
-/*@+incondefs@*/
-#elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
 #include <stdbool.h>
-#endif
 
 /*==== Configuration definitions ====*/
 #ifndef NO_STRDUP