Ensure that our `find_executable` behaves as expected:
* When the executable contains a fully- or partially-qualified filename
component (eg, `foo/bar`) that `PATH` is not searched; these paths are
relative to the current working directory.
* An empty segment in `PATH` (on POSIX systems) is treated as the
current directory; this is for compatibility with Bourne shells.
* When a file exists in `PATH`, it is actually executable (on POSIX)
The POSIX `realpath` function canonicalizes relative paths, symbolic links,
and case (on case-insensitive filesystems). For example, on macOS, if you
create some file `/private/tmp/FOO`, and you call `realpath("/tmp/foo")`,
you get _the real path_ returned of `/private/tmp/FOO`.
To emulate this behavior on win32, we call `GetFullPathName` to handle the
relative to absolute path conversion, then call `GetLongPathName` to handle
the case canonicalization.
Clar handles multiple levels of hierarchy in a test name _but_ it does so
assuming that there are not tests at a parent folder level. In other words,
if you have some tests at path/core.c and path/win32.c, then you cannot have
tests in path.c. If you have tests in path.c, then the things in path/*.c
will be ignored.
Move the tests in path.c into path/core.c.
