libdfp: Implement sysdeps/soft-dfp/bid/numdigits.h

This patch implements the numdigits functions for BID. They are:

- getexpd[32|64|128]: returns the _Decimal expoenent value as int.
- setexpd[32|64|128]: sets the _Decimal expoenent from an int value.
- numdigitsd[32|64|128]: return the number of digits from coefficient.
- setdigitsd[32|64|128]: sets the coefficient value.
- left_justifyd[32|64|128]: left justify the decimal value.
libdfp: implement decode.c for BID encoding

This patch adds the decode.c functions for BID encoding. They are:
* __decoded[32|64|128]: print a string representation of _Decimal
  number.
libdfp: Add software expected ULPs

This patch adds the expected ULPs for current testscase for
software-only implementation.
libdfp: base ABI list for BID encoding
libdfp: add -shared-libgcc

To avoid name clashing with compiler generated symbols for _Decimal
operations and the ones provided by libdfp, the libgcc is now linked as
dynamic.
libdfp: removing uneeded BID implementation

This patch removes the uneeded __host_to_ieee_[32|64|128] BID
implementations.  The endianess is already handled in libdecnumber.
libdef: base-math symbol hidden_def

This patch makes all the libdfp _Decimal operatations (like sum,
multiplication, cast, etc.) have a hidden definition.  This is be able
to create symbol alias and avoid intra-library PLT calls for compiler
generated calls for _Decimal operations.

For instance, on the code:

_Decimal32 foo (_Decimal32 a, _Decimal b)
{
  return a + b;
}

The compiler may emit a call to '__<bid/dpd>_addsd3' if the plaform does
not support hardware instructions.  Since libdfp provides its own
implementation for the symbol, if we dot an alias in the form:

asm ("__<bid/dpd>_addsd3 = <internal symbol name>")

The compiler/linker will eventually create a PLT calls to the add
implementation instead of a local one.
libdfp: Add BID symbol-hacks to avoid PLT calls

This patchs add the BID symbol hack to avoid intra-library PLT calls.
libdfp: Fix DPD symbol hacks to PLT calls

This patch updates the DPD symbols hacks to avoid PLT intra-library
calls to cover the possible symbol created when the library is built
without hardware instructions enabled.
libdfp: Makefile.in flags

This patch clean up the CFLAGS to avoid warning for strtol/strtoll by
using _ISOC99_SOURCE instead of -D_POSIX_C_SOURCE=200809L/-D_SVID_SOURCE.