Change default DEFAULT_TIDY_HEADER_DIRS to empty

* Default -header-filter will now contain only module directory.
  * In a clean build of aosp_x86_64-eng, this change can reduce
    the number of (duplicated) clang-tidy warnings by 77% or more.
* When compiled with WITH_TIDY=1, if DEFAULT_TIDY_HEADER_DIRS is
  not set, warnings from a header file will be shown only if
  the file is in a module's (sub)directory.
* Set DEFAULT_TIDY_HEADER_DIRS="bionic/|bootable/|build/|cts/|\
  dalvik/|developers/|development/|frameworks/|\
  libcore/|libnativehelper/|system/"
  will get before this change's -header-filter.
* Fix a bug: Default header-filter was not added when
  tidy_flags was defined in a module.
  With this fix, some incorrectly hidden header file tidy warnings
  will now show up.

Bug: 179530304
Test: make with WITH_TIDY=1 and various setting of DEFAULT_TIDY_HEADER_DIRS
Change-Id: Ia0c05349908a730862dae36be9a2dbe4f44fb6da