back: find the auxiliary files when GNUSTEP_MAKEFILES is unset (#162)

configure passed the GNUSTEP_MAKEFILES variable straight to
AC_CONFIG_AUX_DIR, but the generated configure searches for config.guess
and config.sub before the shell code that sets GNUSTEP_MAKEFILES from
gnustep-config has run.  With GNUSTEP_MAKEFILES unset in the environment
configure then failed with "cannot find required auxiliary files".

Resolve the makefiles directory inline in the AC_CONFIG_AUX_DIR argument,
the way gnustep-base already does, so the auxiliary files are found whether
or not GNUSTEP_MAKEFILES is set in the environment.  The generated configure
is updated to match.

Author: DTW-Thalion

configure

@@ -2562,7 +2562,11 @@ as_fn_append ac_header_c_list " unistd.h unistd_h HAVE_UNISTD_H"
 ac_aux_files="config.guess config.sub"
 
 # Locations in which to look for auxiliary files.
-ac_aux_dir_candidates="$GNUSTEP_MAKEFILES"
+ac_aux_dir_candidates="`if test -z "$GNUSTEP_MAKEFILES"; then
+  gnustep-config --variable=GNUSTEP_MAKEFILES 2>&5
+else
+  echo $GNUSTEP_MAKEFILES
+fi`"
 
 # Search for a directory containing all of the required auxiliary files,
 # $ac_aux_files, from the $PATH-style list $ac_aux_dir_candidates.

configure.ac

@@ -41,8 +41,15 @@ fi
 
 #--------------------------------------------------------------------
 # Use config.guess, config.sub and install-sh provided by gnustep-make
+# Evaluation order of the configure script means we can not depend on
+# GNUSTEP_MAKEFILES being set for simple variable substitution, so we
+# execute a bit of shell code to dynamically get the directory.
 #--------------------------------------------------------------------
-AC_CONFIG_AUX_DIR($GNUSTEP_MAKEFILES)
+AC_CONFIG_AUX_DIR([`if test -z "$GNUSTEP_MAKEFILES"; then
+  gnustep-config --variable=GNUSTEP_MAKEFILES 2>&5
+else
+  echo $GNUSTEP_MAKEFILES
+fi`])
 
 #--------------------------------------------------------------------
 # Determine the host, build, and target systems