warning: conflicting types for built-in function %qD

[Matt Austern]

In the C front end, when diagnose_mismatched_decls sees a declaration 
of a function whose name is the same as a builtin's but whose types are 
different, we use the declaration we see but we issue a warning.  For 
example:
[isolde:tmp]$ cat foo.c
extern double scalb ( double, int );
[isolde:tmp]$ /work/root.apple/bin/gcc -c foo.c
foo.c:1: warning: conflicting types for built-in function 'scalb'

This warning is unconditional.  As you can see from the above example, 
we don't even need -Wall to see it.  The only way to turn it off, in 
fact, is to use the heavy-handed -w.

What was the rationale behind issuing this warning?  I find it rather 
unfriendly.  In this example, after all, the user isn't doing anything 
wrong.  scalb is not defined in any standard that I can see, and users 
have every right to declare a function called scalb with whatever types 
they like.

Earlier versions of the compiler did not issue this warning, and the 
C++ front end still doesn't.   I'd like to see this warning removed, or 
at the very least tamed.

                        --Matt