rfe: conwert sym wrappers to smart references

[stsp]

c++23 will have smart references.
This will allow us to turn the sym wrappers
into a proxy objects.

[stsp]

Which would mean a gcc compatibility hopefully.
But its quite a big rework.
Whether or not the gcc compatibility worth
the trouble, is an open question. And when
this is going to be implemented in gcc, is difficult
to say.
clang just works...

Related material:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0352r1.pdf
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0416r1.pdf

[stsp]

As became obvious from the failed #166
attempt, such wrappers should be
squashed into AsmXXX classes.

[stsp]

#56 (comment)
#56 (comment)

If we can use smart references, perhaps
the inability to modify temporaries will be
circumvented by relaying an access via an
internal pointer to the child object, rather
than the memcpy() to the inherited self.
#56 will use the explicit lifetime management,
so such pointers might be possible.
It however seems that smart references
are not happening in C++23.