Bootstrap failure on Linux/x86-64 in Ada

[Paolo Bonzini]

> ln: creating symbolic link `x86_64-suse-linux-gnu/stage1-x86_64-suse-linux-gnu' to `stage1-x86_64-suse-linux-gnu': File exists
> make[3]: *** [stage1-start] Error 1
> make[3]: Leaving directory `/builds/gcc/misc'
> make[2]: *** Waiting for unfinished jobs....
> make[2]: *** [configure-build-fixincludes] Error 2
> make[1]: *** [stage2-bubble] Error 2
> make[1]: Leaving directory `/builds/gcc/misc'
> make: *** [bootstrap] Error 2

I believe I have a fix for this race condition as part of unrelated 
changes (which I have to test a bit more).

Paolo