libdfp: Function left_justify fixed for PPC/DPD.

Added a check to left_justify function in order to catch when the
number justified would become a NaN data. This patch also adds tests
to verify this.
libdecnumber: Fix potentially out of the bound array access

decGetInt can potentially acess a out of the bounds value from array
DECPOWERS, this patch fixes the test to actually access the array.
Function left_justify fixed for x86/BID.

Added a check to left_justify function in order to catch when the
number justified would become a NaN number, like is done for PPC
with hardware instructions.

This patch also fixes get_digits[32|64|128] to handle NaN numbers.
libdfp: Add not equal to BID hack alias
libdfp: Fix test internal buffer size
libdfp: Fix NaN1/mask definition for LE/DPD

This patch fixes the NaN1 mask definition on left_justify for LE and
also corrects a compiler warning triggered by issuing memset with size
of 0.
libdfp: Enable BID for 32bits

This patch add BID support for 32 bits.  64 bits support relies on int
128 bits operations which is supplied by GCC/clang extension
__uint128_t.  Some architectures, however, does not support this
extension (x86 32 bits, for instance).

So on BID 32 bits the mini-gmp implementation from libgmp is used.
Currently it is included direct in libdecnumber/decimal128.c object and
thus used in other parts of libdfp through libdecnumber.a static
library.

The mini-gmp is a multiprecision library that works on limbs of 32 bits.
libdecnumber: Fix decDebug64 extension
libdfp: Fix bid-private warning in 32-bits