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

HTMLparser.c

@@ -11,12 +11,9 @@
 #ifdef LIBXML_HTML_ENABLED
 
 #include <string.h>
-#ifdef HAVE_CTYPE_H
 #include <ctype.h>
-#endif
-#ifdef HAVE_STDLIB_H
 #include <stdlib.h>
-#endif
+
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
 #endif