Makefile: Rename TARGET_DIRS to TARGET_LIST

To be more accurate on its purpose and make code that looks for a certain
target out of this variable more readable.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
diff --git a/configure b/configure
index db8c9d8..14b1113 100755
--- a/configure
+++ b/configure
@@ -6128,7 +6128,7 @@
 echo "VERSION=$qemu_version" >>$config_host_mak
 echo "PKGVERSION=$pkgversion" >>$config_host_mak
 echo "SRC_PATH=$source_path" >> $config_host_mak
-echo "TARGET_DIRS=$target_list" >> $config_host_mak
+echo "TARGET_LIST=$target_list" >> $config_host_mak
 if [ "$docs" = "yes" ] ; then
   echo "BUILD_DOCS=yes" >> $config_host_mak
 fi