[build] build fixes for AIX

x-ref:
  "Compile on AIX conflicting types for 'etag_create'"
  https://redmine.lighttpd.net/boards/2/topics/9242

src/etag.h

@@ -4,7 +4,11 @@
 
 #include "buffer.h"
 
+#ifdef _AIX
+#include <sys/stat.h>
+#else
 struct stat;            /* declaration */
+#endif
 
 typedef enum { ETAG_USE_INODE = 1, ETAG_USE_MTIME = 2, ETAG_USE_SIZE = 4 } etag_flags_t;
 

src/mod_webdav.c

@@ -2714,7 +2714,9 @@ webdav_copymove_dir (const plugin_config * const pconf,
         else {
             switch (errno) {
               case EEXIST:
+             #if EEXIST != ENOTEMPTY
               case ENOTEMPTY:
+             #endif
                 if (!overwrite) {
                         webdav_xml_response_status(b, &src->rel_path, 412);
                         return 412; /* Precondition Failed */