This ensures strerror() and friends continue to work correctly even if a
(non-PIE) executable linked against an older libc imports sys_errlist (which
causes sys_errlist to refer to the executable's copy with a size fixed when
that executable was linked).

The executable's use of sys_errlist remains broken because it uses the
current value of sys_nerr and may access past the bounds of the array.

Different from the message "Using sys_errlist from executables is not
ABI-stable" on freebsd-arch, this change does not affect the static library.
There seems no reason to prevent overriding the error messages in the static
library.

Add %M{essage} extension which prints an errno value as the
corresponding string if possible or numerically otherwise.

It is not currently possible to do the syslog(3) like %m extension
because errno would need to get capatured on entry to the first
function in the printf family, so %M requires you to supply errno
as an argument.

Add %Q{uote} extension which will print a string in double quotes with
appropriate back-slash escapes (only) if necessary.