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.
Adapt codegen to removal of old _d_invariant from druntime.

We should think about using symbolic constants for runtime function
names though, this is not maintainable in the long run.
zext bool to i8 in makeLValue.
Fold in out-of-source test build adaption changes.
Handle static array typed SliceExps.

Fixes DMD testcase 'testbounds2'.
Fold in rudimentary rt.sections implementation.
Minor debug log fixes.
Handle side-effects in TupleExp::e0.

Fixes DMD testcase 'aliasthis'.