Continuing the cleanups of libgcc soft-fp configuration for
powerpc*-*-linux* in preparation for implementing
TARGET_ATOMIC_ASSIGN_EXPAND_FENV for soft-float and e500, this patch
optimizes the choice of which functions to build for the e500 cases.

For e500v2, use of hardfp is generally right, except that calls to
__unordsf2 and __unorddf2 are actually generated by GCC from
__builtin_isunordered and so they need to be implemented with soft-fp
to avoid recursively calling themselves.  For e500v1, hardfp is right
for SFmode (except for __unordsf2) but soft-fp for DFmode (and when
using soft-fp, as usual it's best for the conversions between DFmode
and integers all to come directly from soft-fp rather than some coming
from libgcc2.c).  Thus, new variables hardfp_exclusions and
softfp_extras are added that configurations using t-hardfp and
t-softfp can use to achieve the desired effect of selectively mixing
the two sources of functions.

Tested with no regressions for crosses to powerpc-linux-gnuspe (both
e500v1 and e500v2); also checked that the same set of symbols and
versions is exported from shared libgcc before and after the patch.

	* config/t-hardfp (hardfp_exclusions): Document new variable for
	user to define.
	(hardfp_func_list): Exclude functions from $(hardfp_exclusions).
	* config/t-softfp (softfp_extras): Document new variable for user
	to define.
	(softfp_func_list): Add functions from $(softfp_extras).
	* config/rs6000/t-e500v1-fp, config/rs6000/t-e500v2-fp: New files.
	* config.host (powerpc*-*-linux*): For e500v1, use
	rs6000/t-e500v1-fp and t-hardfp; do not use t-softfp-sfdf and
	t-softfp-excl.  For e500v2, use t-hardfp-sfdf, rs6000/t-e500v2-fp
	and t-hardfp; do not use t-softfp-sfdf and t-softfp-excl.

From-SVN: r216835