tests: skip small-stack tests on hppa architecture

tests: skip small-stack tests on hppa architecture

On hppa these tests crash because the allocated stack space is too
small, even after it was doubled in b9a190789 (and the data size
doubled to match) to make it work on powerpc.  For this arch just
skip these tests, which is enough to make the whole suite pass.

Fixes: https://bugs.debian.org/757402
Based-on-patch-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Greg Price <gnprice@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>