Be sure to instantiate the parameters of a function, even when the

function's type is (strictly speaking) non-dependent. This ensures
that, e.g., default function arguments get instantiated properly.

And, since I couldn't resist, collapse the two implementations of
function-parameter instantiation into calls to a single, new function
(Sema::SubstParmVarDecl), since the two had nearly identical code (and
each had bugs the other didn't!). More importantly, factored out the
semantic analysis of a parameter declaration into
Sema::CheckParameter, which is called both by
Sema::ActOnParamDeclarator (when parameters are parsed) and when a
parameter is instantiated. Previously, we were missing some
Objective-C and address-space checks on instantiated function
parameters.

Fixes PR6733.

llvm-svn: 101029