* Use an actual compiler definition to determine whether we have a
floating-point unit or not.
* Use a modern (VFPU) assembly instruction to get/set the fpsr
* If we don't have an fpsr, at least zero out the return value
While there, also modify the install target. We should make sure to
install all openlibm*.h headers. There is still some work to be done:
openlibm_fenv_*.h still depends on some additional bits. I'd propose
that we eventually create an include/openlibm_cdefs.h that contains all
of the macros we need.