Rather than requiring macro implementations to add required whitespace
and indentation, basic format all macro expansions. Right now this uses
the default four space indentation, we can consider having that inferred
later. Macros can opt-out of automatic formatting by implementing
`formatMode` and setting it to `.disabled`.
Also moves the extra newlines before/after expansions to a new "Inline
Macro" refactoring.
Resolves rdar://107731047.
The macro tests were all using "REQUIRES: OS=macosx" as a proxy for
"have the Swift Swift parser". There was an existing feature for this,
but it was just checking whether the path was passed through. Fix that
to use the same variable as in CMake.
Also remove all extraneous `-I` and `-L` to the host libs in the target
invocations.
