Don't check for standard C89 headers

Don't check for

- ctype.h
- errno.h
- float.h
- limits.h
- math.h
- signal.h
- stdarg.h
- stdlib.h
- string.h
- time.h

Stop including non-standard headers

- malloc.h
- strings.h

xmlregexp.c

@@ -23,9 +23,8 @@
 
 #include <stdio.h>
 #include <string.h>
-#ifdef HAVE_LIMITS_H
 #include <limits.h>
-#endif
+
 #ifdef HAVE_STDINT_H
 #include <stdint.h>
 #endif