Make linux-dri-x86-64 more like linux-dri-x86. Add ARCH_FLAGS. This is
where things like "-m64" or "-m32" should be specified. Using this, a
32-bit DRI build can be done on an x86-64 system by doing 'ARCH_CFLAGS=-m32
make linux-dri-x86'. Minor tweaks to linux-dri to support these changes.
Improve the behaviour of the build system wrt depend files.
- Remove the -Y option for makedepend, so that the standard
directories are searched
- No longer pipe the multiple errors that the -Y option caused
into /dev/null -- we want to know about these failures.
- Fix up a few other misc makedepend failures.