* [Concurrency] Build C only libdispatch before Swift on non-Darwin platforms
_Concurrency depends on libdispatch and since it is not available by
default on non-Darwin platforms, it needs to be built before the Swift
project, so that the dependency can be resolved.
* Fix clibdispatch installation and BuildSystem tests
* Fix build system tests on Darwin and formatting
This causes build-script to use the conservative dependency information that I
committed. When one uses this option, it is assumed that one wants to also
install all built products.
Some notes:
1. I included an extra --install-all option so without --infer enabled
one can enable this sort of install everything that we want to
build behavior.
2. I added %cmake as a lit variable. I did this so I could specify in
my build-system unit tests that on Linux they should use the just
built cmake (if we built cmake due to an old cmake being on the
system). Otherwise, the build system unit tests took way too
long. These are meant to be dry-runs, so building this cmake again
is just wasteful and doesn't make sense.
3. I unified how we handle cmark, llvm, swift with the rest of the
build products by making them conditional on build_* variables, but
to preserve current behavior I made it so that they are just
enabled by default unlike things like
llbuild/swiftpm/foundation/etc. This was necessary since previously
we would just pass these flags to build-script-impl and
build-script didn't know about them. Now I taught build-script
about them so I can manipulate these skip-build-{cmark,llvm,swift}
and then just pass them down to build-script-impl if appropriate
rather than relying on build-script-impl to control if these are
built.
Once this lands, I think we are at a good enough place with
build-script until we get rid of build-script-impl in terms of high
value QoI that will imnprove productivity. Once build-script-impl is
destroyed, we can start paring back what build-script itself does.
