While the compiler can bridge C block types to Swift function types,
the Swift runtime cannot. Don't bridge block types to Swift function
types in Objective-C generic arguments, so
NSArray<some-block-type>
will get imported as
[@convention(block) (...) -> Whatever]
rather than
[(...) -> Whatever]
Fixes rdar://problem/40879067 in a fairly narrow way; the Clang
importer's approach to adjusting types based on context needs a
cleanup, but this is the safe, localized fix suitable for 4.2.
d529002009