kheaders: optimize header copy for in-tree builds

This script copies headers by the cpio command twice; first from
srctree, and then from objtree. However, when we building in-tree,
we know the srctree and the objtree are the same. That is, all the
headers copied by the first cpio are overwritten by the second one.

Skip the first cpio when we are building in-tree.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

kernel/gen_kheaders.sh

@@ -56,14 +56,16 @@ fi
 rm -rf $cpio_dir
 mkdir $cpio_dir
 
-pushd $srctree > /dev/null
-for f in $dir_list;
-	do find "$f" -name "*.h";
-done | cpio --quiet -pd $cpio_dir
-popd > /dev/null
+if [ "$building_out_of_srctree" ]; then
+	pushd $srctree > /dev/null
+	for f in $dir_list
+		do find "$f" -name "*.h";
+	done | cpio --quiet -pd $cpio_dir
+	popd > /dev/null
+fi
 
-# The second CPIO can complain if files already exist which can
-# happen with out of tree builds. Just silence CPIO for now.
+# The second CPIO can complain if files already exist which can happen with out
+# of tree builds having stale headers in srctree. Just silence CPIO for now.
 for f in $dir_list;
 	do find "$f" -name "*.h";
 done | cpio --quiet -pd $cpio_dir >/dev/null 2>&1