i386: stand: Retire its own nfs.c, and switch to libsa/nfs.c. NFC

efiboot/x86: Add serial console support via raw I/O port access

Unfortunately, some (most?) UEFI implementations do not support
com ports by ``Serial I/O Protocol''.

``PNP0501-0'' and friends are not recognized also.

In this case, if user explicitly requires to switch to serial
console by ``consdev'' command, try to use raw I/O port access.

Ugly, but what FreeBSD does, at least.

Proposed as PR port-amd64/57523

bsd.own.mk: rename to CC_WNO_ADDRESS_OF_PACKED_MEMBER

Provide a single variable
CC_WNO_ADDRESS_OF_PACKED_MEMBER
with options for both clang and gcc, to replace
CLANG_NO_ADDR_OF_PACKED_MEMBER
CC_NO_ADDR_OF_PACKED_MEMBER
GCC_NO_ADDR_OF_PACKED_MEMBER

Using the convention CC_compilerflag, where compilerflag
is based on the full compiler flag name.

Fix broken flag -nocombreloc, 2.34 did not complain for not understanding it,
but 2.39 wants -z nocombreloc. Is it really needed?

branches: 1.19.4;
Do not pass BIOS geometry when booting using EFI

Recent Mac return garbage data that will crash the code handling it,
and EFI boot does not need it anyway.

add support for new GCC 9 warnings that may be too much to fix
right now. new address-of-packed-member and format-overflow
warnings have new GCC_NO_ADDR_OF_PACKED_MEMBER amd
GCC_NO_FORMAT_OVERFLOW variables to remove these warnings.

apply to a bunch of the tree. mostly, these are real bugs that
should be fixed, but in many cases, only by removing the 'packed'
attribute from some structure that doesn't really need it. (i
looked at many different ones, and while perhaps 60-80% were
already properly aligned, it wasn't clear to me that the uses
were always coming from sane data vs network alignment, so it
doesn't seem safe to remove packed without careful research for
each affect struct.) clang already warned (and was not erroring)
for many of these cases, but gcc picked up dozens more.

Add --noinhibit-exec and --no-dynamic-linker

Add multiboot 2 support to x86 bootloaders

multiboot 2 is required to boot Xen on an EFI system.
This also require a kernel patch for properly discovering
the ACPI RSDP, which is available after 20190912, in
src/sys/arch/x86/acpi/acpi_machdep.c 1.26-1.28

There are a few missing bit in this multiboot 2 implementation
(which are unused by Xen):
- Header tags Address, Freambuffer, and Relocatable are ignored
- Tags APM and Network are not provided
- Tags ACPI old and ACP new are only provided for ACPI boot
- Tag boot device does not provides the subpart (BSD disklabel partition)

Notes:
- multiboot2 is disabled in dosboot, otherwise the binary
gets too big and build fails.
- in src/sys/arch/i386/stand/efiboot, consinit() is renamed
as efi_consinit() to avoid prototype conflicts in src/sys/sys/systm.h

branches: 1.15.2;
Added tftp support to x86 efiboot.

Specify NOLIBCSANITIZER in x86 bootloader-like code under sys/arch/

Set NOLIBCSANITIZER for i386 and amd64 specific bootloader-like code.

branches: 1.13.2;
- Disable MKSANITIZER
- Redo using NOPIE
- Add NORELRO

efiboot: Added network boot support.

efiboot: Added serial console support.

efiboot: system can boot from CD/DVD-ROM media.

branches: 1.9.2; 1.9.8; 1.9.10;
efiboot: Boot parameters can be set via installboot(8).

branches: 1.8.4; 1.8.6;
centralize vers.c building for standalone programs.

branches: 1.7.2;
efiboot: pass memory map after ExitBootService is called to kernel.

Remove unnecessary flag.

branches: 1.5.2;
Unbreak clang again.

Don't error out for set but unused variables for now.

Mark reboot() and _rtt() as __dead.
Use __builtin_unreachable() to ensure Panic really is marked dead.

Thanks to joerg@

Fix build with clang.

Initial commit of native amd64 EFI boot loader.