fix hotspot build failures with -D_FORTIFY_SOURCE=2 and -Wformat=1

[Kelly O'Hair]

Both fwrite() and (void)fwrite() are legal,
the first one is a potential error, but the later
is defined by the standard as having the function return value
explicitly "discarded".

So warning about a value that has been explicitly "discarded" by
the terms of the standard seems like a very questionable warning.

-kto

Andrew Haley wrote:
> Kelly O'Hair wrote:
>> The issue seems so simple to me.
>> If the function return is to be ignored, you make an explicit cast
>> to void. This practice is so old and common I don't understand why
>> it's so complicated.
> 
>> gcc/g++ are not the only compilers on the planet.
>> Writing portable C or C++ code becomes increasingly more complicated
>> when you have to rely on special features of the compiler to get them
>> to shut up about perfectly valid code.
>>
>> What happened to following the standards?
>>
>> WG14/N1124 6.3.2.2 void
>>
>> "... If an expression of any other type is evaluated as a void
>> expression, its value or designator is discarded.
>> (A void expression is evaluated for its side effects.)"
> 
> Huh?  The standard doesn't say that you should not warn about
> legal but potentially problematic code.  That's what most
> warnings are, after all.
> 
> Andrew.