swift234

IRGen: Differentiate between Swift.Bool and ObjCBool

SIL already does this where necessary, except with foreign throwing
functions; this patch changes Sema and the ClangImporter to give
them an ObjCBool foreign error result type explicitly.

This fixes a problem where calls to functions taking and returning
the C99 _Bool type were miscompiled on Mac OS X x86-64, because
IRGen was conflating the Objective-C BOOL type (which is a signed
char on some platforms) and C99 _Bool (which lowers as the LLVM
i1 type).

Fixes <rdar://problem/26506458> and <rdar://problem/27365520>.