tests/sigtramp_test: xfail on non-amd64

This test fail until at least https://reviews.llvm.org/D155066 is
rebased and picked up for aarch64 and more work is done for the other
archs.

PR: 289096
Reviewed by: jlduran
Fixes: fef84fd8ae845e19cec0f6b9aac0e6451cca3d7a
MFC after: 3 days