Log Message:
lang/gcc47: Fix DragonFly32 floating point handling

Like i386-FreeBSD, the i386-DragonFly floating point unit uses a 53-bit
mantissa.  GCC uses the TARGET_96_ROUND_53_LONG_DOUBLE macro to know
which platforms behave this way.

Unfortunately, setting this macro to 1 breaks precision on Ada, and
leaving it at 0 breaks precision on c/c++ long double handling.  However
lang/gcc47 likely will never support Ada, so we'll favor c/c++.  This
is only an issue for i386; the setting on x86_64 should be zero as it
uses 64-bit precision.