cmake: adding $<SEMICOLON> instead of space on zephyr_get_compile_<type>

The current zephyr_get_compile_<type> flags returns compile / include
flags based on generator expressions.

But they also included a space.

This have the unintended side-effect that when the properties are
fetched into another variable and later appended to lists in order to
finally be used in a CMake target function / custom command, then CMake
in some cases will quote the string, creating a quoted argument like:
"arg0 arg1 arg2: instead of individual arguments like: "arg0" "arg1"
"arg2".

By using $<SEMICOLON>, then arguments are seperated correctly.

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