The construction of type refinement contexts performs lazy expansion
for the contents of macro expansions, so that TRC creation doesn't
force all macros to be expanded. However, the logic that skips macro
expansions would *also* skip some declarations produced within a macro
expansion, even when building the TRC specifically for that macro
expansion buffer. This manifest as missing some availability
information within the TRC, rejecting some well-formed code.
Tune the logic for "don't visit macro expansions when building a TRC"
to recognize when we're building a TRC for that macro expansion.
Fixes rdar://128400301.
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.
