Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Second attempt at eliminating .text relocations in shared libraries
compiled with stack protector.

Use libssp_nonshared library to pull __stack_chk_fail_local symbol into
each library that needs it instead of pulling it from libc. GCC
generates local calls to this function which result in absolute
relocations put into position-independent code segment, making dynamic
loader do extra work every time given shared library is being relocated
and making affected text pages non-shareable.

Reviewed by: kib
Approved by: re (kib)

Back out previous revision until better tested fix is ready.

Approved by: re (impliciti, by approving previos check-in)

Eliminate .text relocations in shared libraries compiled with stack protector.

Use libssp_nonshared library to pull __stack_chk_fail_local symbol into
each library that needs it instead of pulling it from libc. GCC generates
local calls to this function which result in absolute relocations put into
position-independent code segment, making dynamic loader do extra work everys
time given shared library is being relocated and making affected text pages
non-shareable.

Reviewed by: kib
Approved by: re (kensmith)

Restore the install location of libssp.so.0.

Noticed by: tegge

Fix build when WITH_SSP is set explicitly.

Submitted by: Jeremie Le Hen

Enable GCC stack protection (aka Propolice) for userland:
- It is opt-out for now so as to give it maximum testing, but it may be
turned opt-in for stable branches depending on the consensus. You
can turn it off with WITHOUT_SSP.
- WITHOUT_SSP was previously used to disable the build of GNU libssp.
It is harmless to steal the knob as SSP symbols have been provided
by libc for a long time, GNU libssp should not have been much used.
- SSP is disabled in a few corners such as system bootstrap programs
(sys/boot), process bootstrap code (rtld, csu) and SSP symbols themselves.
- It should be safe to use -fstack-protector-all to build world, however
libc will be automatically downgraded to -fstack-protector because it
breaks rtld otherwise.
- This option is unavailable on ia64.

Enable GCC stack protection (aka Propolice) for kernel:
- It is opt-out for now so as to give it maximum testing.
- Do not compile your kernel with -fstack-protector-all, it won't work.

Submitted by: Jeremie Le Hen <jeremie@le-hen.org>

Don't forget to clean generated ssp.h.

Update bmake glue to build GCC 4.2.

Also:
Switch FreeBSD to use libgcc_s.so.1.

Use dl_iterate_phdr to locate shared objects' exception frame
info instead of depending on older register_frame_info machinery.
This allows us to avoid depending on libgcc_s.so.1 in binaries
that do not use exception handling directly. As an additional
benefit it breaks circular libc <=> libgcc_s.so.1 dependency too.

Build newly added libgomp.so.1 library, the runtime support
bits for OpenMP.

Build LGPLed libssp library. Our libc provides our own
BSD-licensed SSP callbacks implementation, so this library
is only built to benefit applications that have hadcoded
knowledge of libssp.so and libssp_nonshared.a. When linked
in from command line, these libraries override libc
implementation.