Fix the generation of ListConstants with VPATH
Fix the generation of ListConstants with VPATH

When the build directory differs from the source directory, the
automatic variable '$<' points to the file found by prepending the path.
This causes double '../' to be inserted when combined with
'$(abs_top_srcdir)'. This patch fixes this.

Signed-off-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

apyrgio/ganeti,bitemyapp/ganeti,dimara/ganeti,leshchevds/ganeti,apyrgio/ganeti,ganeti/ganeti,andir/ganeti,yiannist/ganeti,ganeti/ganeti,andir/ganeti,onponomarev/ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,andir/ganeti,dimara/ganeti,mbakke/ganeti,leshchevds/ganeti,mbakke/ganeti,ganeti/ganeti,grnet/snf-ganeti,leshchevds/ganeti,bitemyapp/ganeti,grnet/snf-ganeti,yiannist/ganeti,yiannist/ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti