Trying #include <wctype.h> all the time, too

It was specifically NOT being done under Haiku (which Luc notes
caused a "implicit declaration of function" warning), BeOS (moot?),
macOS (__APPLE__)[*], and Android[*].

[*] I've asked Mark & Pere to check that macOS & Android builds are
still happy.  See tuxpaint-maintainers thread
https://sourceforge.net/p/tuxpaint/mailman/tuxpaint-maintainers/thread/Z-O0V3aa6joXl6zl%40bill-t480s/#msg59165314

src/tuxpaint.c

@@ -277,6 +277,7 @@ char *strcasestr(const char *haystack, const char *needle)
 #endif
 
 #include <wchar.h>
+#include <wctype.h>
 
 #if defined __BEOS__ || defined __HAIKU__ || defined __APPLE__ || defined __ANDROID__
 #include <stdbool.h>
@@ -284,8 +285,6 @@ char *strcasestr(const char *haystack, const char *needle)
 #define FALSE false
 #define TRUE true
 #endif
-#else
-#include <wctype.h>
 #endif
 
 #include <libintl.h>