gcc10's -Wreturn-local-addr gives FP warning about lib/careadlinkat

[Jim Meyering]

Building latest latest coreutils using latest-from-git gcc10 evokes
this false positive:

lib/careadlinkat.c: In function 'careadlinkat':
cc1: error: function may return address of local variable
[-Werror=return-local-addr]
lib/careadlinkat.c:73:8: note: declared here
   73 |   char stack_buf[1024];

I'm guessing improved flow analysis will eventually suppress this. I
hesitate to turn off the useful and normally-high-S/N
-Wreturn-local-addr globally. Maybe just disable it in that one file,
temporarily?