Those are warnings, not errors.
You can see the difference between the regular and back quotes by typing
Code:
echo 'locate -n 1 libperl.so'
echo `locate -n 1 libperl.so`
and seeing the difference in the output. The first is just a quoted string, the second is the output from the actual command.
I don't know which is correct to pass to cmake. It seems like their method of detecting perl should work if you didn't try to override it at all.