title: How do I make `mmm` omit the time-consuming doc build steps?
body: <p>Working with the source code from AOSP, after I make a trivial change to a 
  source file under <code>frameworks/base/core/java/android/</code>,
  <code>mmm frameworks/base -j9</code> takes about 4 minutes.
  A large portion of that time seems to be waiting for steps with names containing "Droiddoc" or "Docs droiddoc" to complete:</p>
  
  <pre><code>...
  [ 14% 4/28] Docs droiddoc: out/target/common/docs/api-stubs
  [ 21% 6/28] //frameworks/base:test-api-stubs-docs Droiddoc [common]
  DroidDoc took 102 sec. to write docs to out/soong/.intermediates/frameworks/base/test-api-stubs-docs/android_common/docs/out
  [ 28% 7/25] Docs droiddoc: out/target/common/docs/api-stubs
  DroidDoc took 113 sec. to write docs to out/target/common/docs/api-stubs
  [ 32% 8/25] //frameworks/base:api-stubs-docs Droiddoc [common]
  DroidDoc took 115 sec. to write docs to out/soong/.intermediates/frameworks/base/api-stubs-docs/android_common/docs/out
  [ 40% 9/22] //frameworks/base:system-api-stubs-docs Droiddoc [common]
  DroidDoc took 117 sec. to write docs to out/soong/.intermediates/frameworks/base/system-api-stubs-docs/android_common/docs/out
  ...
  </code></pre>
  
  <p>I really don't need or want any documentation to be built on every little incremental recompile.
  Is there a way to omit all these doc-related steps?</p>
  
  <p>I'd be interested in either a command line flag if there is one,
  or a hopefully simple hack to one or more Makefiles and/or .mk files.</p>
  
  <p>I've looked through the .mk files; in particular build/make/core/droiddoc.mk
  seems relevant.  I tried cutting some wires in it without really understanding what I was doing, without success.</p>
  
  <p>I'm hoping someone who understands how these .mk files are put together
  will know how to do this easily.</p>
  
  <p>I expect this will be of interest to anyone who runs <code>mmm</code> frequently.</p>