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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Fix spurious and extra underflows and resulting inaccuracies for some cases
with 1 huge component and 1 tiny (but nowhere near denormal) component.
Rescale earlier so that a scale factor of 2 can be combined with a non-
scale divisor of 2, so that the division doesn't shift out a bit. In the
usual case where the scale factor is just 1, the division may shift out a
bit, but then the underflow is not spurious and the inaccuracies are harder
to fix.

Minor cleanups to csqrt*(), mostly in comments.

Remove the STDC CX_LIMITED_RANGE pragma and its verbose comment. We still
don't have any C99 compilers (that support fenv pragmas), and if we did
then there are thousands of other places in libm that would need to use
them more than here.

The other cleanups are smaller.

Fix scaling bugs which gave innaccuracies and spurious underflows in csqrt()
and csqrtl().

When one component is huge and the other is tiny, scaling down the tiny
component gave spurious underflow.

When both components are denormal, not scaling them up gave inaccuracies
of 34+ ulps on not very carefully selected args. Fixing this reduces the
maximum error to 1.6 ulps on the same set of args (mosly not denormal ones).

The scaling used multiplication of a complex variable by 2, but clang messes
this on amd64 up by losing the sign of -0.0. Calculate the components
separately, as is well known to be needed for operations on more exceptional
values.

Add a macro nan_mix() and use it to get NaN results that are (bitwise)
independent of the precision in most cases. This is mainly to simplify
checking for errors. r176266 did this for e_pow[f].c using a less
refined expression that often didn't work. r176276 fixes an error in
the log message for r176266. The main refinement is to always expand
to long double precision. See old log messages (especially these 2)
and the comment on the macro for more general details.

Specific details:
- using nan_mix() consistently for the new and old pow*() functions was
the only thing needed to make my consistency test for powl() vs pow()
pass on amd64.

- catrig[fl].c already had all the refinements, but open-coded.

- e_atan2[fl].c, e_fmod[fl].c and s_remquo[fl] only had primitive NaN
mixing.

- e_hypot[fl].c already had a different refined version of r176266. Refine
this further. nan_mix() is not directly usable here since we want to
clear the sign bit.

- e_remainder[f].c already had an earlier version of r176266.

- s_ccosh[f].c,/s_csinh[f].c already had a version equivalent to r176266.
Refine this further. nan_mix() is not directly usable here since the
expression has to handle some non-NaN cases.

- s_csqrt.[fl]: the mixing was special and mostly wrong. Partially fix the
special version.

- s_ctanh[f].c already had a version of r176266.

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.

Rename cpack*() to CMPLX*().

The C11 standard introduced a set of macros (CMPLX, CMPLXF, CMPLXL) that
can be used to construct complex numbers from a pair of real and
imaginary numbers. Unfortunately, they require some compiler support,
which is why we only define them for Clang and GCC>=4.7.

The cpack() function in libm performs the same task as CMPLX(), but
cannot be used to generate compile-time constants. This means that all
invocations of cpack() can safely be replaced by C11's CMPLX(). To keep
the code building with GCC 4.2, provide copies of CMPLX() that can at
least be used to generate run-time complex numbers.

This makes it easier to build some of the functions outside of libm.

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.

In the line
#pragma STDC CX_LIMITED_RANGE ON
the "ON" needs to be in caps. gcc doesn't understand this pragma
anyway and assumes it is always on in any case, but icc supports
it and cares about the case.

Implement csqrtl().

- Correct the range check in the double version to catch negative values
that would overflow.
- Style fixes and improved handling of NaNs suggested by bde.

Implement and document csqrt(3) and csqrtf(3).