MFC -fno-common fixes: r359389, r359394, r359397-r359399, r359403-r359404,
r359406, r359413-r359416, r359425, r359427, r359432-r359433, r359443,
r359675-r359677

Note: this is not necessarily a complete fix to get these programs to build
with -fno-common applied.

r359389:
config(8): fixes for -fno-common

Move this handful of definitions into main.c, properly declare these as
extern in config.h. This fixes the config(8) build with -fno-common.

Unexplained in my previous commit to gas, -fno-common will become the
default in GCC10 and LLVM11, so it's worth addressing these in advance.

r359394:
MFV r359393: tcsh: import 6974bc35a5cd

This removes an extra variable definition that causes the -fno-common build
to fail, which will be a new default in GCC10/LLVM11.

r359397:
zfs: fix -fno-common issues

A similar (or identical?) fix has already landed in OpenZFS.

-fno-common will become the default in GCC10/LLVM11.

r359398:
sh: remove duplicate el definition

el is declared extern in myhistedit.h and defined in histedit.c. Remove the
duplicate definition in input.c to appease the -fno-common build.

-fno-common will become the default in GCC10/LLVM11.

r359399:
telnet: remove some duplicate definitions, mark terminaltype extern

Most of these were already properly declared and defined elsewhere, this is
effectively just a minor cleanup that fixes the -fno-common build.

-fno-common will become the default in GCC10/LLVM11.

r359403:
Revert 359399: telnet -fno-common bits

There was a large misfire from my local diff that I need to investigate, and
this version committed did not build.

r359404:
Re-apply r359399: telnet -fno-common fix

line and auth_level's redefinitions are just extraneous

telnetd will #define extern and then include ext.h to allocate storage for
all of these extern'd vars; however, two of them are actually defined in
libtelnet instead. Instead of doing an #ifdef extern dance around those
function pointers, just add an EXTERN macro to make it easier to
differentiate by sight which ones will get allocated in globals.c and which
ones are defined elsewhere.

r359406:
telnet: kill off remaining duplicate definition

r359413:
ipfilter: remove duplicate definition of 'thishost'

thishost is already defined in lib/initparse.c; no need for this one. This
fixes the ipfilter build with -fno-common.

-fno-common will become the default in GCC10/LLVM11.

r359414:
iscontrol: move definition of vflag/iscsidev to iscontrol.c

Mark the declaration extern as these are used elsewhere; this fixes the
build with -fno-common.

r359415:
userboot: mark host_fsops as extern

This is already defined elsewhere; mark this declaration extern to the fix
the -fno-common build.

r359416:
systat: remove redundant definition of kd

kd is already properly declared in extern.h and defined in main.c, rendering
this definition useless. This fixes the -fno-common build.

r359425:
locate: fix -fno-common build

Just a single variable declaration to extern and define elsewhere here,
myctype.

-fno-common will become a default in GCC10/LLVM11.

r359427:
fsck_ffs/fsdb: fix -fno-common build

This one is also a small list:

- 3x duplicate definition (ufs2_zino, returntosingle, nflag)
- 5x 'needs extern', 3/5 of which are referenced in fsdb

-fno-common will become the default in GCC10/LLVM11.

r359432:
gdb: compile with -fcommon explicitly

As described in the comment, gdb relies on some of the linker magic that
happens with -fcommon. I suspect the life expectancy of gdb-in-base is low
enough that this isn't worth spending much time addressing, especially given
the vintage. Hit it with the -fcommon hammer so that it continues to just
work.

r359433:
bmake: fix -fno-common build

debug was declared extern, but debug_file was not; correct this and define
debug_file in main.c (as debug is) to fix the -fno-common build.

-fno-common will become the default with GCC10/LLVM11.

r359443:
MFV r359442: bmake: import -fno-common fix build back from upstream

sjg@ committed the local patch previously committed upstream; pull it in to
vendor/ to ease any potential stress of future imports.

r359675:
kqueue tests: fix -fno-common build

vnode_fd and kqfd are both shared among multiple CU; define them exactly
once.

In the case of vnode_fd, it was simply the declaration that needed
correction.

-fno-common will become the default in GCC10/LLVM11.

r359676:
ntpd: fix build with -fno-common

Only a small nit here: psl should be declared extern and defined exactly
once.

-fno-common will become the default in GCC10/LLVM11.

r359677:
yp*: fix -fno-common build

This is mostly two problems spread out far and wide:
- ypldap_process should be declared properly
- debug is defined differently in many programs

For the latter, just extern it and define it everywhere that actually needs
it. This mostly works out nicely for ^/libexec/ypxfr, which can remove the
assignment at the beginning of main in favor of defining it properly.

-fno-common will become the default in GCC10/LLVM11.

MFC r325834,r325997,326502: Move sys/boot to stand/

This is effectively a direct commit to stable/11, due to differences between
stable/11 and head. Changes to DTS in sys/boot/fdt/dts were often
accompanied by kernel changes. Many of these were also risc-v updates that
likely had many more dependencies to MFC.

Because of this, sys/boot/fdt/dts remains as-is while everything else in
sys/boot relocates to stand/.

r325834: Move sys/boot to stand. Fix all references to new location

r325997: Remove empty directories.

r326502: Document the sys/boot -> stand move in hier.7 and the top-level README.

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

Add support for FreeBSD/i386 guests under bhyve.
- Similar to the hack for bootinfo32.c in userboot, define
_MACHINE_ELF_WANT_32BIT in the load_elf32 file handlers in userboot.
This allows userboot to load 32-bit kernels and modules.
- Copy the SMAP generation code out of bootinfo64.c and into its own
file so it can be shared with bootinfo32.c to pass an SMAP to the i386
kernel.
- Use uint32_t instead of u_long when aligning module metadata in
bootinfo32.c in userboot, as otherwise the metadata used 64-bit
alignment which corrupted the layout.
- Populate the basemem and extmem members of the bootinfo struct passed
to 32-bit kernels.
- Fix the 32-bit stack in userboot to start at the top of the stack
instead of the bottom so that there is room to grow before the
kernel switches to its own stack.
- Push a fake return address onto the 32-bit stack in addition to the
arguments normally passed to exec() in the loader. This return
address is needed to convince recover_bootinfo() in the 32-bit
locore code that it is being invoked from a "new" boot block.
- Add a routine to libvmmapi to setup a 32-bit flat mode register state
including a GDT and TSS that is able to start the i386 kernel and
update bhyveload to use it when booting an i386 kernel.
- Use the guest register state to determine the CPU's current instruction
mode (32-bit vs 64-bit) and paging mode (flat, 32-bit, PAE, or long
mode) in the instruction emulation code. Update the gla2gpa() routine
used when fetching instructions to handle flat mode, 32-bit paging, and
PAE paging in addition to long mode paging. Don't look for a REX
prefix when the CPU is in 32-bit mode, and use the detected mode to
enable the existing 32-bit mode code when decoding the mod r/m byte.

Reviewed by: grehan, neel
MFC after: 1 month

Replace all references to loader_callbacks_v1 with loader_callbacks.

Suggested by: grehan@

Add a version of the FreeBSD bootloader which can run in userland, packaged
as a shared library. This is intended to be used by BHyVe to load FreeBSD
kernels into new virtual machines.