title: How to make "ndk-build clean" continue on error
body: <p>I have a large source tree with multiple projects.  One of the projects uses JNI.</p>
  
  <p>When I try to "make clean" on my entire source tree it goes through and removes all the object files and libs.  Then it steps into my applications directory to make clean.</p>
  
  <p>When it gets to my JNI project it executes "ndk-build clean" which fails because the library I link against has been removed as part of the clean:</p>
  
  <pre><code>ndk-build clean
  Android NDK: ERROR:/Users/spartygw/xyz/src/applications/foo/jni/Android.mk:bar: LOCAL_SRC_FILES points to a missing file    
  Android NDK: Check that /Users/spartygw/xyz/src/applications/foo/jni/../../../../lib/libbar.a exists or that its path is correct   
  /Users/spartygw/android-ndk-r6b/build/core/prebuilt-library.mk:43: *** Android NDK: Aborting    .  Stop.
  make[3]: *** [clean_android] Error 2
  make[2]: *** [clean] Error 2
  make[1]: *** [clean] Error 2
  make: *** [clean] Error 2
  </code></pre>
  
  <p>I've tried adding "ndk-build -k clean" and "ndk-build --ignore clean" but it bails out regardless.</p>
  
  <p>How can I make ndk-build ignore the dependency on the libraries that are not yet built and just clean the local objects?</p>