Android: Always add standard include directories last

The logic added in commit v3.6.0-rc1~30^2 (Add a variable to specify
language-wide system include directories, 2016-05-24) to use
`CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES` incorrectly filters them by
`CMAKE_<LANG>_IMPLICIT_INCLUDE_DIRECTORIES`.  Rather than recognizing
this, commit v3.8.0-rc1~60^2 (Android: Pass sysroot include directory
explicitly, 2017-01-20) worked around the problem by incorrectly
removing `/usr/include` from `CMAKE_<LANG>_IMPLICIT_INCLUDE_DIRECTORIES`
so it worked in `CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES`.

By not filtering out `/usr/include` from user-specified include
directories, we allow the code

    include_directories(${CMAKE_SYSROOT}/usr/include)

to place the include directory too early on the command line.

Fix support for standard include directories to not be filtered by
implicit include directories, and do not remove `/usr/include` from the
list of implicit include directories for Android builds.  Add a test
case to verify that an explicit `/usr/include` is ignored in favor
of the standard directory at the end.

Fixes: #17059
Status Job ID Name Coverage
  External
passed ghostflow-branch-check-master

passed ghostflow-commit-check