libdfp: Sync libdecnumber with GCC

This patch syncs the libdecnumber from GCC (git, id
69811c67b5668fd9ff2705e363f1e39f9a337d14) with libdfp one.
libdfp: Fix test-bfp-convertion tests

So test-bfp-convertion convertions assumes that float/double/long double
holds precised values (for instance 12.345) in base 10, where in fact if
the variable is expanded to a more precision value (using prinft or a
multiprecion library) it will hold an different value
(12.345000267028809 in the 12.345 case for float). This patch fixes the
expected value to decimal transformation.
libdfp: Refactor generic isnand

This patch refactor software implementation of isnand[32|64|128] to
use an generic implementation for convert _Decimal[32|64|128] to
words/doublewords.
libdfp: isinfd refactor

This patch refactor software implementation of isinfd[32|64|128] to
use an generic implementation for convert _Decimal[32|64|128] to
words/doublewords.
libdfp: isfinite refactor

This patch refactor software implementation of isfinited[32|64|128] to
use an generic implementation for convert _Decimal[32|64|128] to
words/doublewords.
libdfp: Add llogbd[32|64|128] implementation

This patch adds llogbd[32|64|128] software implementation using
existing ilogbd[32|64|128] implementation . It also adds
[i|l]logb[32|64|128] testcases.
libdfp: Cleanup _IEEE_LIBDFP and _IEEE_LIBM

This patch cleans up the no longer used _IEEE_LIBM and _IEEE_LIBDFP
defines checks. The libdfp library is now built always with errno
support.
libdfp: Add rounding function tests

This patch adds tests for ceil, floor, nearbyint, round, and trunc
functions for _Decimal[32|64|128].
PowerPC: Optimized ceild[32|64|128]
PowerPC: Optimized truncd[32|64|128]
PowerPC: Optimized floord[32|64|128]
PowerPC: optimized nearbyintd[32|64|128]
PowerPC: optimized roundd[32|64|128]
libdfp: Add roundevend[32|64|128] implementation

This patch adds a software implementation for roundeven for
_Decimal[32|64|128]. The function rounds its argument to the
nearest integer value in floating-point format, rounding
halfway cases to even (that is, to the nearest value whose
least significant bit 0), regardless of the current rounding
direction
PowerPC: optimized roundevend[32|64|128]
libdfp: Endian fix for floating point classify

This patch fixes the __dfp_classify_sf and __dfp_classify_df in LE.
libdfp: Add quantumd[32|64|128] software implementation

The quantumdN functions compute the quantum of a finite argument.
If x is infinite, the result is +infinity. If x is NaN, the result
is NaN.
PowerPC: optimized quantumd[32|64|128] implementation
libdfp: Add llquantexpd[32|64|128] software implementation

The llquantexpdN functions compute the quantum exponent of a finite argument.
If x is infinite or NaN, they compute LLONG_MIN and a domain error occurs.
PowerPC: optimized llquantexpd[32|64|128]