MFC r324815: Make elf_aux_info() as public libc function.

- Teach elf aux vector functions about newly added AT_HWCAP and AT_HWCAP2
vectors.
- Export _elf_aux_info() as new public libc function elf_aux_info(3)

The elf_aux_info(3) should be considered as FreeBSD counterpart of glibc
getauxval() with more robust interface.

Note:
We cannot name this new function as getauxval(), with glibc compatible
interface. Some ports autodetect its existence and then expects that all
Linux specific AT_<*> vectors are defined and implemented.

Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

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

Rename aux.c to auxv.c.

On Windows, AUX is the auxiliary device, usually pointing to COM1.
Therefore it is forbidden to create a file named aux.c. To make it a bit
easier for Windows users to check out our source code, rename this file
to auxv.c.

MFC after: 1 month
Discussed with: kib
Suggested by: Eric van Gyzen <eric vangyzen net>

Use struct vdso_timehands data to implement fast gettimeofday(2) and
clock_gettime(2) functions if supported. The speedup seen in
microbenchmarks is in range 4x-7x depending on the hardware.

Only amd64 and i386 architectures are supported. Libc uses rdtsc and
kernel data to calculate current time, if enabled by kernel.

Hopefully, this code is going to migrate into vdso in some future.

Discussed with: bde
Reviewed by: jhb
Tested by: flo
MFC after: 1 month

Fetch the aux vector for the static libc, and use the entries to
initialize the cache of the system information as it was done for the
dynamic libc. This removes several sysctls from the static binary
startup.

Use the aux vector to fill the single struct dl_phdr_info describing
the static binary itself, to implement dl_iterate_phdr(3) for the
static binaries. [1]

Based on the submission by: John Marino <draco marino st> [1]
Tested by: flo (sparc64)
MFC after: 2 weeks

Use aux vector to get values for SSP canary, pagesize, pagesizes array,
number of host CPUs and osreldate.

This eliminates the last sysctl(2) calls from the dynamically linked image
startup.

No objections from: kan
Tested by: marius (sparc64)
MFC after: 1 month