The hppa build failures with GCC 14

[Joseph Myers]

An obstruction to moving build-many-glibcs.py to use GCC 14 by default is 
that the build has been failing for hppa, with a questionable 
-Wstringop-overflow error, since 18 September 2023.

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112358

That PR has details of the jump threading path that apparently involves a 
null pointer being used with an atomic operation.  Could someone try to 
figure out whether this path is actually possible (if so, there's a glibc 
bug to fix; if not, figuring it out should give an appropriate comment we 
can used with DIAG_* macros to disable the error)?

-- 
Joseph S. Myers
josmyers@redhat.com