use saner calculations in should_yield

This is based on feedback from bde.

MFC after:	6 days
gcc: Altivec register adjustments from Apple.

Obtained from:	gcc pre-4.3 (rev. 124763; GPLv2)
MFC after:	3 weeks
gcc: Altivec register adjustments from Apple.

Obtained from:	gcc pre-4.3 (rev. 124763; GPLv2)
MFC after:	3 weeks
Forced commit to note that r258652 is actually:

gcc: Move conditions before an assert.

It is a bit cleaner to check the conditions before calling the assertion.
It also preserves the style from the rest of the code.
This is just a cosmetical change to match better what both Apple's gcc42
and Android's gcc-4.2.1 do.
Fix macro name in comment.
Fix a segfault / internal compiler error.

Among other causes, when gcc throws a warning before parsing any tokens,
the cur_token pointer is at the beginning of malloc'd memory.
Dereferencing cur_token[-1] can cause a segfault.

Code taken from OpenBSD
http://www.openbsd.org/cgi-bin/cvsweb/src/gnu/gcc/libcpp/errors.c
which was a more complete fix than the one I originally coded.

MFC after:	1 week
Fix warnings to not append "No error: 0".

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Hide struct pcb definition by #ifdef __amd64__ braces.  If cc -m32
compilation results in inclusion of the header, a confict arises due
to savefpu being union for i386, but used as struct in the pcb
definition.  The 32bit code should not need amd64 variant of the
struct pcb anyway.

For struct region_descriptor, use __uint64_t instead of unsigned long,
as the base type for bit-fields.  Unsigned long cannot have width 64
for -m32.

The changes allowed to use sys/sysctl.h for cc -m32.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Add an kinfo sysctl to retrieve signal trampoline location for the
given process.

Note that the correctness of the trampoline length returned for ABIs
which do not use shared page depends on the correctness of the struct
sysvec sv_szsigcodebase member, which will be fixed on as-need basis.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
mdoc: sort sections.
Use sysctl KERN_PROC_SIGTRAMP to retrieve the signal trampoline
location for the native amd64 ABI.  This fixes unwinding over the
signal frame after trampoline was moved to the shared page.

The code would be more correct if using sysctl for the target process
instead of inspecting gdb' own trampoline, but the current change is
least intrusive and currently, we always initialize the native ABI
sysvec first, which means that trampoline location for FreeBSD/amd64
ABI is relatively stable.

Similar change will benefit libunwind.

Analyzed by:	avg
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Create /var/cache with mode 0755 instead of 0750.

This directory is used by many third party applications and having
permission 0750 makes it impossible to drop group privileges.

MFC after:	3 days
Fix build, attempt two.
- Nuke a second copy of nfscl_attrcache extern declarations from under
ifdef KDTRACE_HOOKS.  This fixes kernel build with options KDTRACE_HOOKS.
- Fix style inconsistencies.
Allow bhyve and bhyveload to attach to tty devices.

bhyveload: introduce the -c <device> parameter
 to select a tty for output (or "stdio")

bhyve: allow the puc and lpc-com backends to
 accept a tty in addition to "stdio"

When used in conjunction with the null-modem device,
nmdm(4), this allows attach/detach to the guest console
and multiple concurrent serial ports. kgdb on a serial
port is now functional.

Reviewed by:	neel
Requested by:	Almost everyone that has used bhyve
MFC after:	10.0
Document the dvdrom target and NODVD variable, forgotten with r258310.

MFC after:	3 days
Sponsored by:	The FreeBSD Foundation
At great personal risk, change the default for LIB32 from yes to no.  As
mentioned in UPDATING, you can even do it as an as-needed operation after
doing a buildworld/installworld.  You can set WITH_LIB32=yes in make.conf
or src.conf.
[automated] Merge in upstream-github/master