Use DEFAULT_TIDY_HEADER_DIRS env variable.

This variable is a regular expression to be passed as
additional patterns to the -header-filter flag for clang-tidy.
For example, when make with WITH_TIDY=1 DEFAULT_TIDY_HEADER_DIRS="d1/d2|mydir/*"
for a project in external/xyz, clang-tidy will be called with additional flag
  -header-filter=\"(external/xyz|d1/d2|mydir/*)\"

Test: make with WITH_TIDY=1 DEFAULT_TIDY_HEADER_DIRS="d1/d2|mydir/*"
Bug: 32668284
Change-Id: I6051f4f80bc6dbab882bd81435ccbc772772ac63