title: Add pre-build step to android ndk-build module for header dependency?
body: <p>Basically, what I'd like to do in an Android.mk file is:</p>
  
  <pre><code>LOCAL_MODULE := foo
  $(LOCAL_MODULE): pre-build
  pre-build:
      @echo HI
  .PHONY: pre-build
  # ...
  include $(BUILD_SHARED_LIBRARY)
  </code></pre>
  
  <p>The ndk-build system does work for <code>ndk-build foo</code>, and the pre-build step works, but if you use this library in an application, it won't do the pre-build step.</p>
  
  <p>In particular, I'm trying to generate a header file (with version/date stamps etc) that is placed in the path that is used in <code>LOCAL_EXPORT_C_INCLUDES</code> such that modules that consume the library can enjoy the header file.</p>