swift234

[test] Drop -enable-source-import from almost all tests that use IRGen.

-enable-source-import doesn't play nice with debug info, and we want to be
able to run all tests with -g added. The last few tests that require
-enable-source-import could be built with --no-debug-info, or however we
end up spelling that.

rdar://problem/18140021 (most of it)

Swift SVN r22742