Fix missing #define when UNITY_EXCLUDE_FLOAT is used

My unit test doesn't require float so I include the UNITY_EXCLUDE_FLOAT definition as part of my compilation process. But in this case, the compiler is throwing an error due _UF is not defined.

The modification is to wrap _UF and _UD with the "#ifndef UNITY_EXCLUDE_FLOAT" check.  So compiler will not fail at compilation time. 

No sure if there is a better way to do it, probably at different level, at _UF/_UD time(?).