Resolve CVC4_USE_SYMFPU in headers at config-time (#2077)

Resolve CVC4_USE_SYMFPU in headers at config-time (#2077)

As described in issue #2013, we had `#ifdef CVC4_USE_SYMFPU` conditions
in floatingpoint.h, which was problematic when installing the header
files because the definition of `CVC4_USE_SYMFPU` was a compile-flag and
simply including the header files in another project would be missing
that definition. This commit moves floatingpoint.h to a template file
floatingpoint.h.in and substitutes the value of `CVC4_USE_SYMFPU` at
configure-time when generating floatingpoint.h (this is the same
solution that integer.h and rational.h use). I have tested the fix with
the examples provided in #2013 and they work.