Update git submodules

* Update ndk from branch 'master'
  to dd0f579a20d0eac7900bd8bdbe0d875d61dcbf3e
  - Merge changes from topic "libcxx-debug"
    
    * changes:
      Mention libc++ not being stripped in the changelog.
      Add APP_STRIP_MODE and LOCAL_STRIP_MODE.
    
  - Mention libc++ not being stripped in the changelog.
    
    Test: None
    Bug: android/ndk#749
    Change-Id: Id8440efbdadacc43f566577d7cafc0e61cec2595
    
  - Add APP_STRIP_MODE and LOCAL_STRIP_MODE.
    
    These arguments allow the user to specify how their binaries should
    be stripped. APP_STRIP_MODE indicated what to do if LOCAL_STRIP_MODE
    is not set. LOCAL_STRIP_MODE always overrides APP_STRIP_MODE.
    
    The value of this argument is passed directly to the strip command, so
    valid values include anything accepted by strip, but commonly will be
    --strip-debug or --strip-unneeded.
    
    A special value may be used to indicated that the binary should not
    be stripped at all: none. This is helpful for users that want to
    preserve even debug info, perhaps during debugging or to delegate the
    stripping behavior to their packaging system (Studio does this).
    
    Test: ./run_tests.py --filter strip*
    Bug: android/ndk#749
    Change-Id: Ia0748cb7b9b92bcbc164f5156a6ad0e523314be2