file(DOWNLOAD): Relative path in output doesn't follow conventions
Typically, when a path is used as an output in a CMake command and that path is relative, it is usually taken to be relative to the current binary directory. But the file(DOWNLOAD)
command doesn't obey this convention, it instead assumes relative to the working directory (i.e. the directory from which CMake is run). We should make the command follow the same convention as used elsewhere. Fixing this will require a policy.
The fix in !4159 (merged) isn't a cause of this problem, but it does increase the likelihood of people encountering this inconsistency.