[Lightning] On `LIGHTNING_CONFIGURE_IF_NOT_FOUND'

[Ludovic Courtès]

Hi,

I do not understand the rationale behind the behavior of
`LIGHTNING_CONFIGURE_IF_NOT_FOUND' in the case where `lightning.h' is
not found.

In the case where `lightning.h' is not found and `$host_cpu' denotes an
architecture supported by Lightning, the shell variable `lightning' is
set to `yes' and the `AC_CONFIG_LINKS' commands are run, no matter
whether a `lightning' and a `lightning/$cpu_subdir' directory are
available.  This link-creation stage doesn't seem appropriate for
Lightning-using programs.

Instead, I'd rather use a more traditional macro like:

  LIGHTNING_CONFIG([ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])

ACTION-IF-NOT-FOUND would typically be invoked whenever `lightning.h' is
not found.

What do you think?

Thanks,
Ludovic.