-global-regs and -global-floats

[Matthew Fluet]

> Matthew, is it OK to get rid of these switches and the associated Control.xxx
> flags?

You can completely remove -global-regs (that was just a hack to get gcc to
use pseudo-regs as a global array).  

I use Control.globalFloats in order to force floating point CPS constants
into the global array, since I'm currently not planning on inlining
floating point constants into the code-stream.  This translation occurs in
backend.fun, so it can apply to either code-gen.  I could change the
branch on Control.globalFloats to Control.native.  The only reason to keep
the flag around would be to experiment with how much of a performance
impact putting floating point constants into a global array has on the
benchmarks.  That might indicate how important it would be down the line
to use floating point constants from the code-stream.