To keep things consistent with the target and target-variant swiftmodule
files, moving the installation of the binary swift module into
`install_swift_interface`. CMake implicitly generates the target
swiftmodule, but does not know about zippered binaries, so we need to
ensure that the target-variant module is available for installation when
applicable.
In some configurations, libraries are installed under
`<install-prefix>/{libdir}/swift/<platform>/<arch>` and module content
is installed under `<install-prefix>/{libdir}/swift/<platform>`.
This also accounts for the fact that Swift currently looks under
`<install-prefix>/{libdir}/swift_static/**` for the static stdlib
builds.
This patch hooks up the swiftCore library build and gets it installing.
This means that we have library evolution hooked up and vector types.
Building it dynamically found that we had duplicate symbols, so fixed
the swiftDemanglingCR library.
Needed to hook up the availability macros.
The flag configuration is for macOS, so we'll need to go through and
figure out what it should look like for the other platforms too.
