cmake: host-tools fixes for DTC

1. Fix the regular expression used to parse version numbers. This uses
\. and . to parse literal dots; the second one matches any character.
Just use [.] instead in both cases.

2. Don't error out if the installed dtc is too old. It's optional, so
we should just proceed without it. Print a warning instead, and make
it so dts.cmake won't do anything with the installed dtc.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
1 file changed