First, we got several CVR propagation cases wrong, which Eli pointed
out in PR2039.

Second, we didn't propagate address space qualifiers correctly, leading
to incorrect lowering of code in CodeGen/address-space.c.

Third, we didn't uniformly propagate the specifier in the array to the
pointer ("int[restrict 4]" -> "int *restrict").

This adds an ASTContext::getArrayDecayedType member that handles the 
non-trivial logic for this seemingly simple operation.

llvm-svn: 49078