[Bug libffi/64572] r219477 breaks bootstrap on x86_64 darwin

[howarth at bromo dot med.uc.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64572

--- Comment #7 from howarth at bromo dot med.uc.edu ---
(In reply to Richard Henderson from comment #6)
> Created attachment 34432 [details]
> proposed patch
> 
> Should fix both the original report and the testsuite failures.

Confirmed that the proposed patch eliminates both the bootstrap failure on
x86_64-apple-darwin14 and the libffi testsuite failures at both -m32 and -m64.