[PATCH] io: Check at runtime if timestamp supports nanoseconds

[Joseph Myers]

This change has broken the build of the testsuite for Hurd.

support_stat_nanoseconds.c: In function 'support_stat_nanoseconds':
support_stat_nanoseconds.c:56:10: error: 'support' is used uninitialized in this function [-Werror=uninitialized]
   56 |   return support;
      |          ^~~~~~~

https://sourceware.org/pipermail/libc-testresults/2021q2/007729.html

-- 
Joseph S. Myers
joseph@codesourcery.com