[patch] Fix dlclose / exit running in parallel resulting in dtor being called twice

[Paul Pluzhnikov <ppluzhnikov at google dot com>]

Greetings,

This a followup to and fix for the problem discovered in
https://sourceware.org/ml/libc-alpha/2017-09/msg00762.html.

As the test program in above message shows, dlclose running in
parallel with exit currently results in "second" being called twice.

The fix for this is trivial (2 line change in stdlib/exit.c). The
majority of this patch is the test case, which is modified from
original to avoid sleep.

Thanks,

P.S. Not sure what commit message should be for this patch.

-- 
Paul Pluzhnikov

Attachment: glibc-dlclose-exit-race-20170920.txt
Description: Text document