The `ARGC`/`ARGV#` variables in function scope hold the original
arguments with no ;-list flattening. Add a way for functions to
cleanly parse arguments that may contain `;`. This also avoids
extra copying of the arguments.
Co-Author: Brad King <brad.king@kitware.com>
The behaviour of double specified keywords is rather undefined or at
least not clearly documented. This change introduces a strict check and
emits a warning in case a keyword has been specified more than once.
Implement a native `cmake_parse_arguments` command that is fully
compatible with the documented behaviour of the previous implementation.
Leave the CMakeParseArguments module empty but existing for
compatibility.