Use AM_ENABLE_MULTILIB only if with_target_subdir isn't empty

* configure.ac (AM_ENABLE_MULTILIB): Use only if
	${with_target_subdir} isn't empty.
	* configure: Regenerated.

zlib/configure

@@ -2181,7 +2181,8 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
-# Default to --enable-multilib
+if test -n "${with_target_subdir}"; then
+  # Default to --enable-multilib
 # Check whether --enable-multilib was given.
 if test "${enable_multilib+set}" = set; then :
   enableval=$enable_multilib; case "$enableval" in
@@ -2218,6 +2219,7 @@ fi
 
 ac_config_commands="$ac_config_commands default-1"
 
+fi
 
 ac_aux_dir=
 for ac_dir in "$srcdir" "$srcdir/.." "$srcdir/../.."; do
@@ -10403,7 +10405,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 10406 "configure"
+#line 10408 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -10509,7 +10511,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 10512 "configure"
+#line 10514 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H

zlib/configure.ac

@@ -4,7 +4,9 @@ AC_PREREQ(2.64)
 AC_INIT
 AC_CONFIG_SRCDIR([zlib.h])
 
-AM_ENABLE_MULTILIB(, ..)
+if test -n "${with_target_subdir}"; then
+  AM_ENABLE_MULTILIB(, ..)
+fi
 
 AC_CANONICAL_SYSTEM