Do we need some pre-defined RPM macro values that
contain the file extensions for exe and shlib ?

Currently these are usually hardcoded in specs as
"" and ".so" respectively, which usually works...
(and not applicable to spec files that doesn't use
%files for listing names, but instead %files -f)

The values are already available from autoconf as
the "ac_exeext" and "acl_cv_shlibext" variables.
(there's also some variables for object files and
static libs, but OK hardcoding those as .o and .a)

The Mac RPM systems use the %{__soext} macro now,
as mentioned in Bugzilla #133389 for Red Hat RPM.

--anders