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.
c917434a86