Version 10 of gcc enforces -fno-common which breaks a lot of things. This fix reverts to the pre-10 behaviour. The real fix is to clean up stray redefinitions which should be declarations.

This avoids reopening collapsed windows after a large vertical resize.

Fixes #357

Fixes #363 Change-Id: Ic8ad5ccce3935fdf00732d78d3024b535db90447

and not unexpectedly quitting an application. Fixes #360

Missed in 0b349f6f that Bterm is not closing fd.

OpenBSD is using pthreads now, so no need for tas.

Also reduce duplication: makecontext is per-arch not per-os-arch. May fix #353.

It may be that pthreads on NetBSD is now good enough, but the build as written (introduced in 23a2368 at my suggestion) is certainly broken, since both NetBSD.c and pthread.c define the same functions. If NetBSD does support pthreads now, then a few things should happen together: - libthread/sysofiles.sh should drop its top NetBSD case entirely - libthread/NetBSD.c should be deleted - libthread/NetBSD-*-asm.s should be deleted - include/u.h's NetBSD case should define PLAN9PORT_USING_PTHREADS and #include <pthread.h> For now, restore to less clearly broken build.

Linux 2.4 is dead. (The libthread code hasn't worked for Linux 2.4 for a long time.)

Linux.c was for Linux 2.4 and is no longer used directly, only indirectly because NetBSD.c was a 1-line file #including Linux.c. So mv Linux.c NetBSD.c. Also rm Linux-*-asm.s which was for Linux 2.4 as well.

More dead code.