ubsan: disable sigaction test for aarch64

[dvyukov]

Summary

The test seems to segfault on aarch64 with tsan:
https://lab.llvm.org/buildbot/#/builders/179/builds/6662
Reason unknown, needs debugging.

[Caslyn]

Thanks @dvyukov - I hope you don't mind I went ahead and committed this on your behalf.

[cseo]

Actually, this test only fails on aarch64 using GNU ld. With lld, it works fine: https://lab.llvm.org/buildbot/#/builders/185/builds/4357

compiler-rt/test/ubsan/TestCases/Misc/Linux/sigaction.cpp

 // RUN: %clangxx -fsanitize=undefined -shared-libsan %s -o %t && %run %t 2>&1 | FileCheck %s
 
 // Ensure ubsan runtime/interceptors are lazily initialized if called early.
 
+// The test seems to segfault on aarch64 with tsan:
+// https://lab.llvm.org/buildbot/#/builders/179/builds/6662
+// Reason unknown, needs debugging.
+// XFAIL: target=aarch64{{.*}}
+
 #include <assert.h>
 #include <signal.h>
 #include <stdio.h>
 
 __attribute__((constructor(0))) void ctor() {
   fprintf(stderr, "INIT\n");
   struct sigaction old;
   assert(!sigaction(SIGSEGV, nullptr, &old));