kbuild: dummy-tools: avoid tmpdir leak in dummy gcc

When passed -print-file-name=plugin, the dummy gcc script creates a
temporary directory that is never cleaned up. To avoid cluttering
$TMPDIR, instead use a static directory included in the source tree.

Fixes: 76426e23 ("kbuild: add dummy toolchains to enable all cc-option etc. in Kconfig")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/dummy-tools/gcc

@@ -96,12 +96,8 @@ fi
 
 # To set GCC_PLUGINS
 if arg_contain -print-file-name=plugin "$@"; then
-	plugin_dir=$(mktemp -d)
-
-	mkdir -p $plugin_dir/include
-	touch $plugin_dir/include/plugin-version.h
-
-	echo $plugin_dir
+	# Use $0 to find the in-tree dummy directory
+	echo "$(dirname "$(readlink -f "$0")")/dummy-plugin-dir"
 	exit 0
 fi