When we setup a command to run, e.g. $FOO we typically set this to just a path to a binary, e.g. /usr/bin/foo. However, this is not necessarily true. On Windows, this can be prefixed by the $FIXPATH prefix, and on all platforms we are allowed to pass arguments to the executable.

If we want to test if this binary actually exists, we need to extract the binary name from this command line. We have a NOFIXPATH argument to UTIL_LOOKUP_PROGS, which tried to resolve this, but it is not enough, and it makes it impossible to both lookup a program properly and also check for its existance afterwards.

Instead, I propose to add a UTIL_GET_EXECUTABLE function that extracts just the path to the binary from such a command.