Fix PR15293: ARM codegen ice - expected larger existing stack allocation

[Stepan Dyatkovskiy]

Hello Renato,

 > If you have that kind of time and are willing to go the full length

I'm not sure about time, since I don't know some pitfalls, may be. But I 
still want try to fix llvm and clang :-)

You say it was fixed once and rejected then. Did somebody guys remember 
some thread names or revisions, may be?

Thanks,
-Stepan.