Merge dmd upstream 237ca3fbe

Merge dmd upstream 237ca3fbe

Backports a fix where a bad cast to TypeFunction resulted in memory
corruption.  The logic in the function semantic has been fixed, and
casts have been replaced with a function call to always check the
front-end AST node value.

Reviewed-on: https://github.com/dlang/dmd/pull/9054

From-SVN: r267207