Some distributions--Debian and Alpine tested--put libusb.h under the
libusb-1.0 directory. Test for its presence and if found define
HAVE_LIBUSB_1_0_LIBUSB_H. Also test for HAVE_LIBUSB or
HAVE_LIBUSB_1_0_LIBUSB_H and conditionally include the correct header
file in the sources.
Android makefile fragments are distributed as extra distribution files
by the GNU build system but are otherwise ignored. The Android build
support is independent and does not rely on the GNU build system.
See android/README.android for more info.
Signed-off-by: Nate Bargmann <n0nb@n0nb.us>