Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFC r235264: MFi386: improve argument passing via btxldr

MFC r232263:

Define several extra macros in bsd.sys.mk and sys/conf/kern.pre.mk, to
get rid of testing explicitly for clang (using ${CC:T:Mclang}) in
individual Makefiles.

Instead, use the following extra macros, for use with clang:
- NO_WERROR.clang (disables -Werror)
- NO_WCAST_ALIGN.clang (disables -Wcast-align)
- NO_WFORMAT.clang (disables -Wformat and friends)
- CLANG_NO_IAS (disables integrated assembler)
- CLANG_OPT_SMALL (adds flags for extra small size optimizations)

As a side effect, this enables setting CC/CXX/CPP in src.conf instead of
make.conf! For clang, use the following:

CC=clang
CXX=clang++
CPP=clang-cpp

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Upgrade our copy of llvm/clang to r126079, from upstream's trunk.

This contains many improvements, primarily better C++ support, an
integrated assembler for x86 and support for -pg.

Use -Wl,-N instead of the undocumented -N option for GCC.

GCC forwards the -N flag directly to ld. This flag is not documented and
not supported by (for example) Clang. Just use -Wl,-N.

Submitted by: Pawel Worach

Remove ifdef PC98.

Start the dreaded NOFOO -> NO_FOO conversion.

OK'ed by: core

MFi386: revisions from 1.15 to 1.17.

MFi386: Get rid of unnecessary use of m4(1) by using cpp(1) instead.

Repocopied by: joe

MFi386: Factor out -nostdlib and use PROG.

MFi386: Cleanups to sys/boot makefiles.

Initiate deorbit burn for the i386-only a.out related support. Moves are
under way to move the remnants of the a.out toolchain to ports. As the
comment in src/Makefile said, this stuff is deprecated and one should not
expect this to remain beyond 4.0-REL. It has already lasted WAY beyond
that.

Notable exceptions:
gcc - I have not touched the a.out generation stuff there.
ldd/ldconfig - still have some code to interface with a.out rtld.
old as/ld/etc - I have not removed these yet, pending their move to ports.
some includes - necessary for ldd/ldconfig for now.

Tested on: i386 (extensively), alpha

Synced with following files:
src/sys/boot/i386/Makefile.inc 1.1
src/sys/boot/i386/btx/btx/btx.s 1.15
src/sys/boot/i386/btx/btxldr/Makefile 1.8
src/sys/boot/i386/btx/btxldr/btxldr.s 1.9
src/sys/boot/i386/libi386/biosdisk.c 1.29
src/sys/boot/i386/loader/Makefile 1.42
src/sys/boot/i386/loader/main.c 1.18
(entry point address of loader was not changed.)

Reviewed by: nyan

$Id$ -> $FreeBSD$

PC98 version of new boot loader. Because boot2 has not yet ported,
files in boot2 directory are copies from legacy biosboot.

Submitted by: IMAI Takeshi <take-i@ceres.dti.ne.jp>