gdtoa wins the award for "most outdated endianness naming convention"
with its IEEE_8087 vs IEEE_MC68k defines. I had a good chuckle.
Update softfloat and arith.h to adjust to BE or LE automatically
based on the low level preprocessor defines.
Fixes printf/scanf on PowerPC64LE, although there is still a problem
lurking regarding Signalling NaNs...
Sponsored by: Tag1 Consulting, Inc.
The settings in arith.h were not fully defined on powerpc64 after the gdtoa
switchover. Generate them using arithchk.c, similar to what AMD64 did for
r114814.
Technically, none of this is necessary in FreeBSD gdtoa, but since the other
platforms have full definitions, we might as well have full definitions
too.
Approved by: jhibbits (in irc)
Differential Revision: https://reviews.freebsd.org/D22775
