[v3] Possible fix for PR 5730

[Gabriel Dos Reis]

Phil Edwards <phil@jaj.com> writes:

| > | > Now, I realize the macro __FAST_MATH__ may not be defined with
| > | > definite value -- that is really sad.  
| 
| I believe you are mistaken here.  It's defined exactly as if you had written
| 
|     #define __FAST_MATH__
| 
| in normal code, i.e., the value is 1 by default.

But that is insufficiant for use in the code I posted.  The reason
being that when it is not defined you get a hard error.

-- Gaby