This commit merges changes that were developed in the "racket7" repo.
See that repo (which is no longer modified) for a more fine-grained
change history.
The commit includes experimental support for running Racket on Chez
Scheme, but that "CS" variant is not built by default.
Detangle the target and host DLL and library directories by
making `get-lib-search-dirs` and `get-dll-dir` report the
host system's directories, and add `get-cross-lib-search-dirs`
and `get-cross-dll-dir`.
A new `-C`/`--cross` flag causes `racket` to save a host config and
collection directory and make them available via `(find-system-path
'host-{config,collects}-dir)`, while plus `(system-type 'cross)`
reports whether `-C` mode is in effect. Besides making the host paths
available, this change allows a same-platform build to run in
corss-platform mode.
The immediate problem to solve was the creation of Windows installers
on Windows, where recent changes to support 'gui-bin-dir configuration
need a clear distinction between the host Racket and the target Racket
being built, even if they're the same platform. (The "GRacket.exe"
executable didn't work, for example.)
The changes in this commit are more than needed for the immediate
problem, but they naturally build on the necessary `-C` flag, and they
support cross-platform package setup where native libraries are needed
during setup.
Although "macOS" is the correct name for Apple's current desktop OS,
we've decided to go with "Mac OS" to cover all of Apple's Unix-like
desktop OS versions. The label "Mac OS" is more readable, clear in
context (i.e., unlikely to be confused with the Mac OSes that
proceeded Mac OS X), and as likely to match Apple's future OS names
as anything.
Adjust installation tools to support cross-installation (i.e.,
installation for a platform other than the current one) as triggered
by "system.rktd" in "lib" having different information than the
running Racket executable.
