swift234

Sema: Fix type member lookup if generic signature validation fails

When validateGenericFuncSignature() returns true, finalizeGenericParamList()
is never called. Name lookup, via PartialGenericTypeToArchetypeResolver would
return a dependent member type of the generic type parameter type, not an
archetype as expected in this case. This would later on lead to a crash in
ReplaceDependentTypes if the function body contained a reference to such a
member type.

Fix this by marking the GenericTypeParamDecls as invalid in this case, and
returning an ErrorType from PartialGenericTypeToArchetypeResolver if given
an invalid GenericTypeParamDecl.

While we're at it, there was an unused isInvalid local variable in
TypeCheckDecl::visitFuncDecl(). It was written to but never read. Replace
the writes with calls to setInvalid().

Fixes <rdar://problem/19620340>.

Swift SVN r30632