Compatibility of modules across releases

[Akim Demaille]

I have a simple question: what is the scheme that is chosen for binary
incompatibility between releases of m4?

I have a concrete examples: I'm toying with something named dumpstat
which currently merely counts the number of invocations of a macro,
which means I have changed the struct macro and struct builtin.  So I
guess it means my modules are incompatible with natural modules.

Maybe some day this will become a --profile supported by m4 itself.
So it might be an incompatibility between 1.5 and 1.6.  How will we
handle this?  Probably by changing the name of libexec, but I just
wanted to know what's the clean means to do that.

I have another concrete example: I also have changed __line__ and
__file__ so that __file/line__(MACRO) expands to the file/line where
the MACRO was defined.  Again, this means some low level structs have
changed, hence, I guess, binary incompatibilities.