For reasons explained in the commit contents, in order to build the
native gnat package for x86_64-darwin, the native gnatboot package for
x86_64-darwin must have access to both the Clang integrated assembler
and the cctools GNU assembler for that platform. This commit creates a
package with both of those assemblers that x86_64-darwin gnatboot can
then be wrapped with.
82b88d2db6