Tweak the assert in ModuleBuilder from r224533 (PR21989)

Turns out there will be left-over deferred inline methods if there have
been errors, because in that case HandleTopLevelDecl bails out early.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224649 91177308-0d34-0410-b5e6-96231b3b80d8
Don't drop attributes when checking explicit specializations.

Consider a template class with attributes on a method, and an explicit
specialization of that method:

    template <int>
    struct A {
      void foo() final;
    };

    template <>
    void A<0>::foo() {}

In this example, the attribute is `final`, but it might also be an
__attribute__((visibility("foo"))), noreturn, inline, etc. clang's current
behavior is to strip all attributes, which for some attributes is wrong
(the snippet above allows a subclass of A<0> to override the final method, for
example) and for others disagrees with gcc.

So stop dropping attributes. r95845 added this code without a test case, and
r176728 added the code for dropping attributes on parameters (with tests, but
they still pass).

As an additional wrinkle, do drop dllimport and dllexport, since that's how
these two attributes work. (This is covered by existing tests.)

Fixes PR21942.

The approach is by Richard Smith, initial analysis and typing was done by me.

With this, clang also matches GCC and EDG on all attributes Richard tested.


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224651 91177308-0d34-0410-b5e6-96231b3b80d8
Driver: refactor a local variable

Pull out a getToolChain() into a local variable to share the call across to all
the uses.  NFC.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224653 91177308-0d34-0410-b5e6-96231b3b80d8
Driver: hoist an assertion

Remove an unnecessary conditional, hoisting the assertion.  Minor style
tweaks/reflowing.  NFC.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@224654 91177308-0d34-0410-b5e6-96231b3b80d8