sandbox_linux_unittests: add sigaltstack to IsSyscallForTestHarness

The ASan runtime started calling it after
https://github.com/llvm/llvm-project/commit/6b4aeec94afc3626c19ed93dea5d158fbea29732

Bug: 1097067
Change-Id: Ifb37700e5385158cf957c987018f1a9561cc0cef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2254318
Auto-Submit: Hans Wennborg <hans@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780312}

sandbox/linux/integration_tests/bpf_dsl_seccomp_unittest.cc

@@ -177,7 +177,9 @@ bool IsSyscallForTestHarness(int sysno) {
   // UBSan_vptr checker needs mmap, munmap, pipe, write.
   // ASan and MSan don't need any of these for normal operation, but they
   // require at least mmap & munmap to print a report if an error is detected.
-  if (sysno == kMMapNr || sysno == __NR_munmap || sysno == __NR_pipe) {
+  // ASan requires sigaltstack.
+  if (sysno == kMMapNr || sysno == __NR_munmap || sysno == __NR_pipe ||
+      sysno == __NR_sigaltstack) {
     return true;
   }
 #endif