Android.bp: Introduce libminikin_defaults

Create an alias for common C++ compiler flags. This CL prepares for
switching to C++20.

Bug: 260725458
Change-Id: If4cf0f0e773371430539cde914bcc761b26acf7e
Signed-off-by: Bart Van Assche <bvanassche@google.com>
7 files changed