swift234

[test] Make sure incremental build tests are actually testing -incremental.

Not having a build record entry in the output file map TURNED OFF
incremental mode. Somehow most of these tests continued to pass.

This commit mechanically adds the right entry in the output file map to
make incremental builds work, and tests that we don't have any warnings
when trying to build the first configuration of each test.

Swift SVN r28750