>> I am not sure how hard it'd be to avoid errors during configure. Are we
>> sure PKG_* macros or other external things will never use AC_MSG_ERROR ?
> In principle ac macros always have an "what if not found" part which
> allows us to fallback nicely.
Note that if you decide to take this approach, it is important that
neither the configure nor the make fail.
Alternatively, it is possible for me to build a sandbox sub-configure
within MPICH2 that'll fork/exec the hwloc configure directly and check
its exit status before deciding whether to include hwloc or not. This,
however, assumes that hwloc will either fail in configure or the library
will be successfully built and might return an error during
initialization. But even in this case "make" should not fail.
Personally, I'd prefer the first approach, but can do with the second
approach as well.