[Sema] Don't allow applying address-of operator to a call to a function
with __unknown_anytype return type.
When the following code is compiled, Sema infers that the type of
__unknown_anytype is double:
extern __unknown_anytype func();
double *d = (double*)&func();
This triggers an assert in CodeGenFunction::EmitCallExprLValue because
it doesn't expect to see a call to a function with a non-reference
scalar return type.
This commit prevents the assert by making VisitUnaryAddrOf error out if
the address-of operator is applied to a call to a function with
__unknown_anytype return type.
rdar://problem/
20287610
Differential revision: https://reviews.llvm.org/D26808
llvm-svn: 287410