[RFA] Fix float argument passing in inferior function calls for ppc64

[Jim Blandy]

Have you folks ever seen this paper?

    http://www.eecs.harvard.edu/~nr/pubs/staged-abstract.html

    We present staged allocation, a technique for specifying calling
    conventions by composing tiny allocators called stages. A
    specification written using staged allocation has a precise, formal
    semantics, and it can be executed directly inside a
    compiler. Specifications of nine standard C calling conventions range
    in size from 15 to 30 lines each. An implementation of staged
    allocation takes about 250 lines of ML or 650 lines of C++. Each
    specification can be used not only to help a compiler implement the
    calling convention but also to generate a test suite.

It seems like an interpreter for this language would take very little
effort to implement in GDB, and could save quite a bit of effort.