Revert "Fix variable pathname spacing"

[kilograham]

This reverts commit 1abda4c.

That commit changes upstream files that have not themselves been changed, which might be ok if we changed them to what they will be, but the changes are I think majorly heavy-handed

I suspect only variables passed as args to get_filename_component or other functions need to be quoted.

set(FOO ${BAR}) is totally fine.

[lurch]

See also "upstream discussions" in raspberrypi/pico-sdk#2349 and FreeRTOS/FreeRTOS-Kernel#1255
And #164 was the PR in this repo that added the commit that's being reverted here.