Merge the 2.063 frontend.
Never make functions without body available_externally.
Removed obsolete importprot members.
Removed last bit of interpret.c diff.
Unions are always static since Issue 9244.
More trivial DMD diff reduction.
Call Expression::init() during startup.

Was added in 2.063.
Work around invalid special ref var initializations in 2.063.
Handle explicit AddrExp for naked asm memory references.
Expression::optimize everything to resolve manifest constants in inline asm.
Never emit naked functions as available_externally.
Extended DtoLinkage comments.
Initial, incomplete ClassReferenceExp::toConstElem implementation.

Allows us to get through a Phobos build without errors.