Remove the CSU support for mips.

Sponsored by:		Netflix

Unlike lld, ld.bfd doesn't infer the emulation from the first object
file, but assumes its compiled in default for ld -r.

Differential Revision:	https://reviews.freebsd.org/D25728

Reviewed by:	kib
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D25537

The ELF notes compiled in C were placed in a section with the wrong type
(SHT_PROGBITS instead of SHT_NOTE).  Previously, sed was used on the
generated assembly to rewrite the section type.  Instead, write the notes
in assembly which permits setting the correct section type directly.

While here, move inline assembly entry points out of C and into assembly
for aarch64, arm, and riscv.

Reviewed by:	kib
Tested on:	amd64 (cirrus-ci), riscv64
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D25211

This makes statically linked binaries with ifuncs operational.

Reported and tested by:	mjg
Reviewed by:	emaste, markj
Sponsored by:	The FreeBSD Foundation
Approved by:	re (rgrimes)
Differential revision:	https://reviews.freebsd.org/D17363

On most architectures crt objects are compiled in a multiple-step process
so that sed can be run on the generated assembly.  As the final step,
the C compiler generates an object file from the modified assembly output.
Currently this last step uses $CC with only $ACFLAGS.  However, for other
uses in the tree, $ACFLAGS is meant to include assembly-specific compiler
flags that are in addition to $CFLAGS (see default .S.o rules
bsd.suffixes.mk).  In particular, external toolchains may require
additional flags to select a non-default target which will be present
in CFLAGS but not ACFLAGS.  To support this while still mitigating the
issue with CFLAGS described in r234502, include a modified CFLAGS that
excludes "-g" when assembling the modified assembly files.

Note that normally an assembler ($AS) is used to assemble .s flags to
object files (see bsd.suffixes.mk).  However, llvm-based toolchains do
not currently have a stand-alone assembler.

Reviewed by:	imp
Sponsored by:	DARPA / AFRL
Differential Revision:	https://reviews.freebsd.org/D10085

This implifies pathing in make/displayed output

MFC after:    3 weeks
Sponsored by: Dell EMC Isilon

FILES is not used when LIBRARIES_ONLY is set, which is used to build and
install the lib32 sysroot.  All of the csu files do quality as "libraries"
for this case so just undefine LIBRARIES_ONLY.

This is still better than the previous realinstall handling as it does
not hook into META_MODE properly.

Sponsored by:	EMC / Isilon Storage Division

This partially reverts r270170 for lib/csu/i386 while retaining the
change for using bsd.lib.mk.

These FILES groups could go into lib/csu/Makefile.inc but I've kept them
in the Makefiles for clarity.

Sponsored by:	EMC / Isilon Storage Division

way: first they are compiled to assembly, then some sed'ing is done on
the assembly, and lastly the assembly is compiled to an object file.

This last step is done using ${CC}, and not ${AS}, because when the
compiler is clang, it outputs directives that are too advanced for our
old gas.  So we use clang's integrated assembler instead.  (When the
compiler is gcc, it just calls gas, and nothing is different, except one
extra fork.)

However, in the .s to .o rules in lib/csu/$ARCH/Makefile, I still passed
CFLAGS to the compiler, instead of ACFLAGS, which are specifically for
compiling .s files.

In case you are using '-g' for debug info anywhere in your CFLAGS, it
causes the .s files to already contain debug information in the assembly
itself.  In the next step, the .s files are also compiled using '-g',
and if the compiler is clang, it complains: "error: input can't have
.file dwarf directives when -g is used to generate dwarf debug info for
assembly code".

Fix this by using ${ACFLAGS} for compiling the .s files instead.

Reported by:	jasone
MFC after:	1 week