Proper Overflow and Underflow

A combination of store-reload and scaling satisfies
the strict semantics.

Store-reload
Unfortunately, basically, shuJIT does this.
In the context of `strictfp', shuJIT disables one of peephole optimizations that prevents the store-reload.

Scaling
For multiplication and division of floating-point numbers,
         shuJIT generates a native code which do the scaling.

Ex.)   For   `a ÷ b'   in double precision,  the compiler generates
                       a   × 2 ** -16382-(-1022)   ÷ b   × 2 ** +16382+(-1022)
                  to make an underflow occur at the proper threshold.