added gu_is_space in gu/utf8.h. this helps to avoid the dependency on the broken unicode library for C.

src/runtime/c/gu/utf8.h

@@ -37,4 +37,10 @@ gu_utf8_decode(const uint8_t** utf8);
 void
 gu_in_utf8_buf(uint8_t** buf, GuIn* in, GuExn* err);
 
+bool
+gu_is_space(uint8_t c) {
+	return (c == '\t' || c == '\n' || c == '\v' ||
+	        c == '\f' || c == '\r' || c == ' ');
+}
+
 #endif // GU_UTF8_H_