libgcc, bitint: do not use softfp_wrap for bitint and add build option

libgcc, bitint: do not use softfp_wrap for bitint and add build option

This patch circumvents the softfp_wrap for bitint functions in libgcc as certain
ports, like arm, can use softfp_wrap to distinquigh between targets they want to
use specialized assembly functions for and targets that they use the soft-fp
C implementations for.  This is an orthogonal choice to the use of the soft-fp
C implementations for bitint conversions.

This patch also adds extra options to build bitint soft-fp functions, this is
needed by the arm port to build HF bitint conversion functions.

libgcc/ChangeLog:

	* config/t-softfp: Don't use softfp_wrap for bitint functions.
	(softfp_cflags): New parameter that is passed to the building of bitint
	functions.