This allows to build and use IEEE modules on Darwin PowerPC.

libgfortran/ChangeLog:

	* config/fpu-macppc.h (new file): initial support for powerpc-darwin.
	* configure.host: enable ieee_support for powerpc-darwin case,
	set fpu_host='fpu-macppc'.

Signed-off-by: Sergey Fedorov <vital.had@gmail.com>