moved all of the downloaded and generated stuff to a single folder

This makes the separation between our source code and everything else
much cleaner. It also makes it easier to ignore all of the output code
etc etc. The deploy etc commands haven't been tested yet, but I don't
think I broke them.
diff --git a/aos/build/tools_config b/aos/build/tools_config
new file mode 100644
index 0000000..653c1ef
--- /dev/null
+++ b/aos/build/tools_config
@@ -0,0 +1,14 @@
+# This is a shell fragment that sets up variables related to where the tools
+# that download_externals.sh downloads so build.sh can use.
+
+EXTERNALS=${AOS}/../output/downloaded
+COMPILED=${EXTERNALS}/../compiled-i386
+
+NINJA_RELEASE=v1.4.0
+NINJA_DIR=${EXTERNALS}/ninja-${NINJA_RELEASE}
+NINJA=${NINJA_DIR}/ninja
+
+# From chromium@154360:trunk/src/DEPS.
+GYP_REVISION=1738
+GYP_DIR=${EXTERNALS}/gyp-${GYP_REVISION}
+GYP=${GYP_DIR}/gyp