[darwin] testsuite/gcc.c-torture/execute/builtins/string-1,3,5,6 failure fix

[Andreas Tobler]

Hi,

we could fix the failures (on darwin HEAD) in the testsuite if we add a 
x file with the content below.

If correct, shall I apply the fixes?

I'd appreciate any feedback on this.

Thanks,
Andreas

if { [istarget "powerpc-*-darwin*"]  } {
         set additional_flags "-multiply_defined suppress"
}
return 0