test: create a link to the generated hw/xfree86/sdksyms.c at build time

test: create a link to the generated hw/xfree86/sdksyms.c at build time

Automake 1.14 gives us warning about source code specified in _SOURCES
that comes from directories other than the current one. It suggests to enable
the subdir-objects feature which only supports code in sub directories.

The test directory needs source from hw/xfree86 which is neither under test
nor under a sub directory of test. In 1.14 we get a warning, in 2.0 it will
break as it will overwrite the object code in xfree86.

The solution in this case is to create a link to hw/xfree86/sdksyms.c at build
time. It's just like any other built source file.

There are no links created in git.

Signed-off-by: Gaetan Nadon <memsize@videotron.ca>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>