cmake: MWDT linker command list fix.

This commit fixes an issue where the list returned by
zephyr_get_include_directories_for_lang() would be a space separated
list, cause the arguments to be quoted during linking.

This is fixed by requesting `$<SEMICOLON>` to be used as separated which
which again ensures a correct expansion of the list.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>