build: apply the distcheck tricks used in xf86-input-evdev

With this change it is possible to complete "make distcheck" safely on the
module, as it no longer tries to write to system directories.

Since synaptics also installs a configuration file, xorg-conf-dir also
needs to be overridden during distcheck.

Signed-off-by: Diego Elio Pettenò <[email protected]>
Signed-off-by: Peter Hutterer <[email protected]>
2 files changed