Fix diagnostics for C-style cast to function type.

If the C-style type cast is applied to the overloaded
function and the destination type is function type,
then Clang will crash with assertion failure.  For example,

    void foo(int);
    void foo(int, int);
    void bar() {
        typedef void (ft)(int);
        ft p = (ft)foo;
    }

In this case, the overloaded function foo will be cast to
a function type, which should be considered as an error.
But, unfortunately, since the function resolution is using
canonical type, the matched function will be returned, and
result in SEGV.

This patch fixes this issue by removing the assertion and
add some error diagnostics as the one in static_cast.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206133 91177308-0d34-0410-b5e6-96231b3b80d8
Improve error recovery around colon.

Parse of nested name spacifier is modified so that it properly recovers
if colon is mistyped as double colon in case statement.
This patch fixes PR15133.

Differential Revision: http://llvm-reviews.chandlerc.com/D2870


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206135 91177308-0d34-0410-b5e6-96231b3b80d8