This flag has been set on startup since 65618fdda0f272a823e6701966421bdca0efa301.
However, This causes some of the math-related tests to fail as they report
zero instead of a tiny number. This fixes at least
/usr/tests/lib/msun/ldexp_test and possibly others.
Additionally, setting this flag prevents printf() from printing subnormal
numbers in decimal form.
See also https://www.openwall.com/lists/musl/2021/02/26/1

PR:		253847
Reviewed By:	mmel
Differential Revision: https://reviews.freebsd.org/D28938

This is already defined by the ncurses headers, so just undef it before
defining it again.

This caused LDBL_MANT_DIG to not be defined and therefore the scalbnl
alias was not being emitted for double==long double platforms.

Fixes:		760b2ffc ("Update scalbn* functions to the musl versions")
Reported by:	Jenkins

Avoid including machine/console.h when bootstrapping on non-FreeBSD.

This happens if -DBOOTSTRAP_ALL_TOOLS or when building on non-FreeBSD.

Mainly link errors interrupts should only be activated on fully linked port,
otherwise noise on lanes can cause livelock. But we don't have error
counters yet, so leave these interrupts disabled.

We could just use a C implementation using __builtin_fabs(), but using
this assembly version guarantees that there is no additional prolog/epilog
code. Additionally, clang generates worse code for masking off the top bit
than GCC: https://bugs.llvm.org/show_bug.cgi?id=49377.

This fixes the RISCV64 softfloat world build after cf97d2a1dab8. That commit
added -fno-builtin to the msun tests which resulted in the first references to
fabs (previously the compiler inlined all calls).

Reviewed By:	dim
Reported by:	mjg
Differential Revision: https://reviews.freebsd.org/D28994

Also updated the logic to use subprocess.run() instead of the old
subprocess.getoutput() which also includes stderr and therefore
can trigger an exception inside Path().exists().

Reported by:	gnn

Instead of copying the code as 00646ca2047305fce32d99edc7a8e6dfd801f3b4
did, include the implementation with the function name re-defined.

The only diff compared to musl is a minor change to scalbnl() to replace
musl's union ldshape with union IEEEl2bits.
This fixes the scalbn tests on non-x86 (since x86 has an assembly version
that is used instead).

Musl commit messages:
commit 8c44a060243f04283ca68dad199aab90336141db
Author: Szabolcs Nagy <nsz@port70.net>
Date:   Mon Apr 3 02:38:13 2017 +0200

    fix scalbn when result is in the subnormal range

    in nearest rounding mode scalbn could introduce double rounding error
    when an intermediate value and the final result were both in the
    subnormal range e.g.

      scalbn(0x1.7ffffffffffffp-1, -1073)

    returned 0x1p-1073 instead of 0x1p-1074, because the intermediate
    computation got rounded to 0x1.8p-1023.

    with the fix an intermediate value can only be in the subnormal range
    if the final result is 0 which is correct even after double rounding.
    (there still can be two roundings so signals may be raised twice, but
    that's only observable with trapping exceptions which is not supported.)

commit 2eaed464e2080d8321d3903b71086a1ecfc4ee4a
Author: Szabolcs Nagy <nsz@port70.net>
Date:   Wed Sep 4 15:52:54 2013 +0000

    math: use float_t and double_t in scalbnf and scalbn

    remove STRICT_ASSIGN (c99 semantics is assumed) and use the conventional
    union to prepare the scaling factor (so libm.h is no longer needed)

commit 1b77b9072f374bd26eb0574b83a0d5f18d75ec60
Author: Szabolcs Nagy <nsz@port70.net>
Date:   Thu Aug 15 10:07:46 2013 +0000

    math: minor scalbn*.c simplification

commit c4359e01303da2755fe7e8033826b132eb3659b1
Author: Szabolcs Nagy <nsz@port70.net>
Date:   Tue Nov 13 10:55:35 2012 +0100

    math: excess precision fix modf, modff, scalbn, scalbnf

    old code was correct only if the result was stored (without the
    excess precision) or musl was compiled with -ffloat-store.
    now we use STRICT_ASSIGN to work around the issue.
    (see note 160 in c11 section 6.8.6.4)

commit 666271c105e4137bdfa195e217799d74143370d4
Author: Szabolcs Nagy <nsz@port70.net>
Date:   Tue Nov 13 10:30:40 2012 +0100

    math: fix scalbn and scalbnf on overflow/underflow

    old code was correct only if the result was stored (without the
    excess precision) or musl was compiled with -ffloat-store.
    (see note 160 in n1570.pdf section 6.8.6.4)

commit 8051e08e10d2b739fcfcbc6bc7466e8d77fa49f1
Author: nsz <nsz@port70.net>
Date:   Mon Mar 19 10:54:07 2012 +0100

    simplify scalbn*.c implementations

    The old scalbn.c was wrong and slow, the new one is just slow.
    (scalbn(0x1p+1023,-2097) should give 0x1p-1074, but the old code gave 0)

Reviewed By:	dim
Differential Revision: https://reviews.freebsd.org/D28872

This also fixes a typo in the dup test that caused the head function to
not be called. On my test system without python3 the tests are now
skipped instead of failing.

Reviewed By:	kp
Differential Revision: https://reviews.freebsd.org/D28903