kbuild: simplify GCC_PLUGINS enablement in dummy-tools/gcc

With commit 1e860048 ("gcc-plugins: simplify GCC plugin-dev
capability test") applied, this hunk can be way simplified because
now scripts/gcc-plugins/Kconfig only checks plugin-version.h
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/dummy-tools/gcc

@@ -75,16 +75,12 @@ if arg_contain -S "$@"; then
 	fi
 fi
 
-# For scripts/gcc-plugin.sh
+# To set GCC_PLUGINS
 if arg_contain -print-file-name=plugin "$@"; then
 	plugin_dir=$(mktemp -d)
 
-	sed -n 's/.*#include "\(.*\)"/\1/p' $(dirname $0)/../gcc-plugins/gcc-common.h |
-	while read header
-	do
-		mkdir -p $plugin_dir/include/$(dirname $header)
-		touch $plugin_dir/include/$header
-	done
+	mkdir -p $plugin_dir/include
+	touch $plugin_dir/include/plugin-version.h
 
 	echo $plugin_dir
 	exit 0