lib/msun: Cleanup after $FreeBSD$ removal

Remove no longer needed explicit inclusion of sys/cdefs.h.

PR: 276669
MFC after: 1 week

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

Work around bogus old gcc "initializer element is not constant" error

After df3b437c1e073eb83e9a93af1c417f3ee8d0de3b, older gcc's such as
4.2.1 (still used on earlier branches for e.g. mips and powerpc) and
6.3.0 (still used for some cross-builds) started throwing bogus errors
like:

In file included from /workspace/src/lib/msun/src/s_llround.c:11:0:
/workspace/src/lib/msun/src/s_lround.c:54:31: error: initializer element is not constant
static const type dtype_min = type_min - 0.5;
^~~~~~~~
/workspace/src/lib/msun/src/s_lround.c:55:31: error: initializer element is not constant
static const type dtype_max = type_max + 0.5;
^~~~~~~~

Since 'type_min' and 'type_max' are constants declared just above these
lines this error is nonsensical, but older gcc's are not smart enough.

Work around the error by reusing the (type)DTYPE_MIN and (type)DTYPE_MAX
macros, so I can MFC this right away, unbreaking a few stable builds.

MFC after: immediately

Fix failures in libm's lround_test after clang 12 import

It turned out that the (type)DTYPE_MAX conversions at the top of
s_lround.c are now emitted as cvtsi2sd instructions, at least on SSE
capable CPUs. This caused the FE_INEXACT flag to always be set, at least
for the double and float variants. Under clang 11, the whole INRANGE()
comparisons were still optimized away, but this has "improved" in clang
12, due to stricter adherence to the -ffp-exception-behavior=maytrap
compiler flag.

To avoid run-time integer to float conversions, use static constants
instead, so they are computed at compile time, and the INRANGE()
statements are optimized away again, if applicable.

While here, use an integer instead of a floating type to store the test
results in lround_test.c, as this is more appropriate, and we can also
drop the volatile hack.

Reported by: arichardson
MFC after: 3 days

msun: Silence new harmless -Wimplicit-int-float-conversion warnings

Clang from trunk recently added a warning for when implicit int-to-float
conversions cause a loss of precision. The code in question is designed
to be able to handle that, so add explicit casts to silence this.

Submitted by: James Clarke <jrtc27@jrtc27.com>
Reviewed by: dim
Obtained from: CheriBSD
MFC after: 1 week
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D21913

lib: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using mis-identified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Create the altix project branch. The altix project will add support
for the SGI Altix 350 to FreeBSD/ia64. The hardware used for porting
is a two-module system, consisting of a base compute module and a
CPU expansion module. SGI's NUMAFlex architecture can be an excellent
platform to test CPU affinity and NUMA-aware features in FreeBSD.

- Import the HEAD csup code which is the basis for the cvsmode work.

Fix a (coincidentally harmless) bug.

Add MI implementations of [l]lrint[f]() and [l]lround[f]().

Discussed with: bde