Fixes rdar://problem/14776565 (AnyObject lookup for Objective-C
properties with custom getters) and rdar://problem/17184411 (allowing
__attribute__((swift_name("foo"))) to work on anything).
Specifically, method requirements that become unnecessary because they
get superseded by the subscript they imply. Fixes
rdar://problem/21420656.
Swift SVN r30194
This is required to correctly use the mock SDK when the SDK overlay is
built and tested separately. (Otherwise, the mock SDK might not get
used, because the overlay SDK options would expand from the
%-substitution, appear first on the command line, and shadow the mock
SDK in the search path).
Swift SVN r25185