MFC r305855, r306297, r306300, r306312-r306313

When MAKEOBJDIRPREFIX points to a case-insensitive file system, the
build can break when different source files create the same object
files (case-insensitivity speaking). This is the case for object
files compiled with -fpic and shared libraries. The former uses
an extension of ".So", and the latter an extension ".so". Rename
shared object files from *.So to *.pico to match what NetBSD does.

Also:
o Compile _Exit.c as C99_Exit.c, as it conflicts with _exit.s
o Add entry to UPDATING
o Document .pico extension

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Follow-up r297842: Rework header generation to fix always rebuilding.

This reworks the handling of common headers to just include the needed
logic rather than invoke MAKE. This avoids the problem listed in r297842
and avoids other dependency tracking issues.

Pointyhat to: bdrewery
Reported by: Nikolai Lifanov <lifanov@mail.lifanov.com>
Sponsored by: EMC / Isilon Storage Division

META_MODE: Avoid changed build command every build.

Because the file is generated with -f using another Makefile, 2
different Makefiles are trying to handle the .meta file for the
target. The obvious .NOMETA_CMP or .NOMETA on the ${MAKE} targets
don't work as they are very limited in scope in bmake. Using
.PHONY fixes the problem and ensures that the ${MAKE} command
is always ran to check if it is outdated in the sub-make.

An example of the problem in gnu/lib/libgcc (with make -dM):
/usr/obj/root/git/freebsd/gnu/lib/libgcc/tm.h.meta: 2: a build command has changed
TARGET_CPU_DEFAULT="" HEADERS="options.h i386/biarch64.h i386/i386.h i386/unix.h i386/att.h dbxelf.h elfos-undef.h elfos.h freebsd-native.h freebsd-spec.h freebsd.h i386/x86-64.h i386/freebsd.h i386/freebsd64.h defaults.h" DEFINES="" /bin/sh /root/git/freebsd/gnu/lib/libgcc/../../../contrib/gcc/mkconfig.sh tm.h
vs
(cd /root/git/freebsd/gnu/lib/libgcc; make -f /root/git/freebsd/gnu/lib/libgcc/../../usr.bin/cc/cc_tools/Makefile MFILE=/root/git/freebsd/gnu/lib/libgcc/../../usr.bin/cc/cc_tools/Makefile GCCDIR=/root/git/freebsd/gnu/lib/libgcc/../../../contrib/gcc tm.h)
Skipping meta for tm.h: .NOMETA
(cd /root/git/freebsd/gnu/lib/libgcc; make -f /root/git/freebsd/gnu/lib/libgcc/../../usr.bin/cc/cc_tools/Makefile MFILE=/root/git/freebsd/gnu/lib/libgcc/../../usr.bin/cc/cc_tools/Makefile GCCDIR=/root/git/freebsd/gnu/lib/libgcc/../../../contrib/gcc tm.h)
`tm.h' is up to date.

Sponsored by: EMC / Isilon Storage Division

DIRDEPS_BUILD: Regenerate without local dependencies.

These are no longer needed after the recent 'beforebuild: depend' changes
and hooking DIRDEPS_BUILD into a subset of FAST_DEPEND which supports
skipping 'make depend'.

Sponsored by: EMC / Isilon Storage Division

Add META_MODE support.

Off by default, build behaves normally.
WITH_META_MODE we get auto objdir creation, the ability to
start build from anywhere in the tree.

Still need to add real targets under targets/ to build packages.

Differential Revision: D2796
Reviewed by: brooks imp

Remove MK_ARM_EABI, the armeb issues have been fixed. The code to support
the oabi is still in the tree, but it is expected this will be removed
as developers work on surrounding code.

With this commit the ARM EABI is the only supported supported ABI by
FreeBSD on ARMa 32-bit processors.

X-MFC after: never
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D876

Make sure that the sub-makes for unwind.h start from the CURDIR
(/usr/src) tree rather than the OBJDIR (/usr/obj) tree. This fixes
broken incremental builds with the canonical MAKESYSPATH workaround
of .../share/mk. This is a gross kludge.

Use src.opts.mk in preference to bsd.own.mk except where we need stuff
from the latter.

Spell NO_PROFILE= as MK_PROFILE=no.

Add compiler support for the ARM EABI.

ARM EABI support is disabled by default and can be enabled by setting
WITH_ARM_EABI when building, however only the kernel-toolchain target will
work with this flag until the rest of the support is added.

Compile libgcov without stack protection. It can be linked into
both static and dynamic binaries compiled with or without stack
protection and should not depend on libssp_nonshared.a symbols.

Discussed with: kib
PR: bin/139052

Compile static gcov library with -fPIC to match what stock GCC builds
are doing. This is required for libgcov.a to be usable on amd64.

Reported by: stas

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.

Convert NO_PROFILE and NO_LIB32 to new style.

NODOCCOMPRESS -> NO_DOCCOMPRESS
NOINFO -> NO_INFO
NOINFOCOMPRESS -> NO_INFOCOMPRESS
NOLINT -> NO_LINT
NOPIC -> NO_PIC
NOPROFILE -> NO_PROFILE

For variables that are only checked with defined(), don't provide
any fake value.

Add libgcov, a runtime support library for binaries compiled for basic
block profiling.