xbps-src: fix fetch phase with depends, performance improvements.

- The fetch phase *must* run after installing pkg dependencies,
  otherwise it could fail if we need them for fetching.

- Performance improvements for xbps-src. Only source shutils files
  at the start, not every time we use a function.

xbps-src/shutils/common_funcs.sh

@@ -141,7 +141,6 @@ msg_red()
 msg_error()
 {
 	msg_red "$@"
-	. $XBPS_SHUTILSDIR/builddep_funcs.sh
 	autoremove_pkg_dependencies
 
 	exit 1