Restore the previous commit which somehow passed the buildbot given a
missing condition on the sub-configure for libdispatch. This makes it
more explicit as to what the desire is; the variable was being used to
serve as a proxy for whether the build is not on a Darwin target.
This flag was being used as an alias for whether or not the host is
non-Darwin. Rather than adding custom checks for this, use the explicit
check that CMake supports. This simplifies the logic and avoids the
proliferation of custom variables which can become confusing for others
who are not familiar with the custom build infrastructure.
When building in a unified build and building the host tools with a
non-clang compiler, we switch compilers. In such a case, we need to
actually add an explicit dependency on the new compiler.
Add a shared library with a C API that provides access to the syntactic parser with callbacks for the inference of raw syntax nodes.
This is primarily intended to be used by SwiftSyntax to speed-up source code parsing for it.
