Most tests were using %swift or similar substitutions, which did not
include the target triple and SDK. The driver was defaulting to the
host OS. Thus, we could not run the tests when the standard library was
not built for OS X.
Swift SVN r24504
New rules for the driver (first match):
1. -repl: no input files allowed
2. -parse-sil: one input file allowed
3. -parse-as-library: any number of input files, all treated as Library
4. one input, extension is .sil: treated as SIL
5. one input: treated as Main
6. many inputs: treated as Library by default; "main.swift" is treated as Main
If we want more control here we can also add a -main-file option to explicitly
call out the main source file, but this at least unblocks building an entire
app target (like ListMaker) with a single Swift invocation.
Swift SVN r9890
