MFC r274922:

Fix the following -Werror warning from clang 3.5.0, while building the
ath kernel module:

sys/dev/ath/ath_hal/ar5212/ar5212_reset.c:2642:7: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
                if (abs(lp[0] * EEP_SCALE - target) < EEP_DELTA) {
                    ^
sys/dev/ath/ah_osdep.h:74:18: note: expanded from macro 'abs'
#define abs(_a)         __builtin_abs(_a)
                        ^
sys/dev/ath/ath_hal/ar5212/ar5212_reset.c:2642:7: note: remove the call to '__builtin_abs' since unsigned values cannot be negative
sys/dev/ath/ah_osdep.h:74:18: note: expanded from macro 'abs'
#define abs(_a)         __builtin_abs(_a)
                        ^
1 error generated.

This warning occurs because both lp[0] and target are unsigned, so the
subtraction expression is also unsigned, and calling abs() is a no-op.

However, the intention was to look at the absolute difference between
the two unsigned quantities.  Introduce a small static function to
clarify what we're doing, and call that instead.

Reviewed by:	adrian
Differential Revision: https://reviews.freebsd.org/D1212
MFC r275366:

Pull in r209785 from upstream libc++ trunk (by Marshall Clow):

  Fix a problem exposed by r208825, which caused bind (and other bits of
  libc++) to stop working. And tests

This fix is needed to support clang 3.5.0 and higher, which are more
strict about forming pointer-to-function types with cv-qualifiers or
ref-qualifiers.  See also the upstream PR <http://llvm.org/PR19742> and
<http://llvm.org/viewvc/llvm-project?rev=208825&view=rev>

Reported by:	amdmi3