Fix the build for amd64.

Even though the files are installed only if "compat" is set, the
/usr/include/g++/bits directories are unconditionally created via
the mtree files.
having more than one line with the same group name and gid is not only
allowed, it's even recommended for groups with lots of members, so
do not warn about duplicate group name lines if the gid is the same
Introduce a variable for security.conf, default empty, to list users
whose home is (allowed to be) owned by another user.

It's a separate variable and not just check_passwd_permit_dups so I can
make security shut up about my uucp users.

Fixes the second half of PR misc/36063
XXX: gcc initialization (mc68k gcc-4.5.x gcc-4.8.x)
revert previous, will turn off globally.
turn off another gcc warning for m68k
gcc 4.8 issues:
- avoid running over the end of an array (this is a real bug, but
  i didn't really look closely at what memory is clobbered.  it
  may not actually matter.)
- move variables inside their #if usage.
Fix build problems.
Add missing declarations for SSP versions of stpcpy(3) and stpncpy(3).
Fix build problem caused by definition of SSP version of stpcpy(3).
correctly fix stpcpy
revert previous now that the config test is correct
Don't attempt to build "stpcpy.c" and "stpncpy.c". NetBSD provides these
functions and these implementation don't build because of the new
SSP definitions.
Revert my last change. I'm not convinced it is correct and while it seems
to fix some build problems it might cause others.
Directories are created even when gcc=48 is not true, so remove
that flag as well.
fix unused variables
avoid confusion with 68010 and 68020. The sun3 always was a 68020, and
the code assumes that.
Make /usr/include/g++/bits/i386 and x86_64 not depend on gcccmds.
mention template instantiation workaround
Grammar fix.