Update git submodules

* Update prebuilts/build-tools from branch 'master'
  to 9867042b2ca10d3e718ad60927efe9af25b8f994
  - Add m4 to the prebuilt build-tools
    
    Bug: 117561006
    Test: OUT_DIR=out DIST_DIR=dist prebuilts/build-tools/build-prebuilts.sh
    Change-Id: Ic44d3640e9bbdc776a93dd2f44a767b082bc7c21
    
diff --git a/prebuilts/build-tools b/prebuilts/build-tools
index 0a35eb9..9867042 160000
--- a/prebuilts/build-tools
+++ b/prebuilts/build-tools
@@ -1 +1 @@
-Subproject commit 0a35eb93833e4003197be7f01d36b7deed225e4b
+Subproject commit 9867042b2ca10d3e718ad60927efe9af25b8f994