toolchain: Add Android specific update scripts

Pulls in shaderc dependency automatically.
diff --git a/buildAndroid/shaderc_revision b/buildAndroid/shaderc_revision
new file mode 100644
index 0000000..04b2324
--- /dev/null
+++ b/buildAndroid/shaderc_revision
@@ -0,0 +1 @@
+53cf6692879c6dcd5f4ccdffb8c10bb17b5e9d55