On MSVC, <stdbool.h> is always needed, apparently

Author: jan.nijtmans

generic/tclInt.h

@@ -68,7 +68,7 @@
 #include <stdarg.h>
 #include <stdlib.h>
 #include <stdint.h>
-#if defined(__STDC_VERSION__) && __STDC_VERSION__ < 202311L
+#if defined(_MSC_VER) || (defined(__STDC_VERSION__) && (__STDC_VERSION__ < 202311L))
 #include <stdbool.h>
 #endif
 #include <string.h>