Log Message:
Switch SDL2 to the standard autotools build system.  Upstream considers
the CMake build system to be experimental.  This gets us working joystick
support on NetBSD, avoids installing bogus headers, and moves us to a sane
library major (which is highly unlikely to ever change again).  Bump
PKGREVISION to 5 and set BUILDLINK_ABI_DEPENDS accordingly.

Recursive revbump coming up.

While here, tidy up this package's options a bit:
- instead of providing six (!) options for standard modern X libraries,
  simply lump them all into the existing x11 option
- provide a dbus option