libdecnumber: Fix decDebug64 extension
libdfp: Enable BID for 32bits

This patch adds BID support for 32 bits. BID current relies on 128-bit
type support, which is supplied by GCC/clang extension __uint128_t.
Some architectures, however, does not support this extension
(x86 32 bits, for instance).

In these case the mini-gmp implementation from libgmp is used to supply
a multiprecision math library (set to emulate a 128-bit int type).
Currently it is included direct in libdecnumber/decimal128.c object and
thus used in other parts of libdfp through libdecnumber.a static
library.