[compiler-rt] [safestack] Silent overflow.c test on aarch64

The safestack overflow.c test is currently failing on an aarch64
buildbot with a segfault, but it is currently passing on other
configuration.

This patch silent the issue for now on aarch64 by setting to all
supported architectures the 'stable-runtime' configure and set
the test to requires it.

llvm-svn: 255491