bootstrapping gnat GCC on amd64

[xorquewasp at googlemail.com]

Just an update.

Finally managed to get the i386 -> amd64 compiler to compile
gcc 4.4.0. It took a few Makefile patches as for some reason,
cross compilation breaks gnatmake.

About to try to get the amd64 compiler to compile itself and
run the test suite.

Added a system-freebsd_x86_64.ads profile and checked all the
other references to freebsd in the source.

I've scripted the entire bootstrap process so it should be
easy to produce binaries for a port.

xw