php: enabled mbstring by default as it does not require external deps.

develop/php/php.conf

@@ -28,6 +28,10 @@ var_append confopt ' ' "--with-config-file-path=$sysconfdir"
 # sockets does not need any external lib. We have to enable it explicitly
 var_append confopt ' ' "--enable-sockets"
 
+# mbstring is also selfcontained and nice to have around
+var_append confopt ' ' "--enable-mbstring"
+var_append confopt ' ' "--enable-mbregex"
+
 for x in zlib bzip2:bz2 curl openssl libmhash:mhash gettext \
 libjpeg:jpeg-dir libpng:png-dir freetype1:ttf; do
     if pkginstalled "${x%:*}"; then