RFR: Handle confstr version lookup failures gracefully

[David Holmes]

On 12/04/2017 10:00 AM, Mikael Vidstedt wrote:
>
> During bootstrapping, os::Linux::libpthread_init() tries to discover the versions of (g)libc and libpthread respectively. This is done using confstr(3). However, musl doesn’t implement support for version discovery, so confstr will return 0/EINVAL.
>
> This change makes the code handle confstr failures gracefully, and defaults using the string “unknown” if the version information cannot be looked up.
>
> http://cr.openjdk.java.net/~mikael/webrevs/portola/glibcversion/webrev.01/hotspot/webrev/

There was no need to separate out the declaration here:

  504   size_t n;
  505
  506   n = confstr(_CS_GNU_LIBC_VERSION, NULL, 0);

Overall I don't think this change is quite what we would want in that it 
is wrong to print "unknown" when in fact there is no libc (or 
libpthread?) involved. And we would surely want to see that we are using 
musl.

Thanks,
David

> Cheers,
> Mikael
>