improve ctype.h macros to diagnose errors

the casts of the argument to unsigned int suppressed diagnosis of
errors like passing a pointer instead of a character. putting the
actual function call in an unreachable branch restores any diagnostics
that would be present if the macros didn't exist and functions were
used.

include/ctype.h

@@ -28,12 +28,12 @@ static __inline int __isspace(int _c)
 	return _c == ' ' || (unsigned)_c-'\t' < 5;
 }
 
-#define isalpha(a) ((((unsigned)(a)|32)-'a') < 26)
-#define isdigit(a) (((unsigned)(a)-'0') < 10)
-#define islower(a) (((unsigned)(a)-'a') < 26)
-#define isupper(a) (((unsigned)(a)-'A') < 26)
-#define isprint(a) (((unsigned)(a)-0x20) < 0x5f)
-#define isgraph(a) (((unsigned)(a)-0x21) < 0x5e)
+#define isalpha(a) (0 ? isalpha(a) : (((unsigned)(a)|32)-'a') < 26)
+#define isdigit(a) (0 ? isdigit(a) : ((unsigned)(a)-'0') < 10)
+#define islower(a) (0 ? islower(a) : ((unsigned)(a)-'a') < 26)
+#define isupper(a) (0 ? isupper(a) : ((unsigned)(a)-'A') < 26)
+#define isprint(a) (0 ? isprint(a) : ((unsigned)(a)-0x20) < 0x5f)
+#define isgraph(a) (0 ? isgraph(a) : ((unsigned)(a)-0x21) < 0x5e)
 #define isspace(a) __isspace(a)
 #endif