Move mako project from the Garnet manifest.

Mako is now used as part of the build to generate GN files for Zircon.

Change-Id: I62e26ebe68b6a16c5cd8e9ca79967535a458b1f1
diff --git a/build b/build
index 86790d3..24ef4e9 100644
--- a/build
+++ b/build
@@ -27,6 +27,10 @@
              githooks="manifest/git-hooks"/>
 
     <!-- Third-party -->
+    <project name="third_party/mako"
+             path="third_party/mako"
+             remote="https://fuchsia.googlesource.com/third_party/mako"
+             gerrithost="https://fuchsia-review.googlesource.com"/>
     <project name="third_party/pyyaml"
              path="third_party/pyyaml"
              remote="https://fuchsia.googlesource.com/third_party/pyyaml"