Enable use_sigaltstack=1 for ASan builds. This will ease the stack overflow detection.

sandbox/linux/seccomp-bpf-helpers/baseline_policy.cc

Index: sandbox/linux/seccomp-bpf-helpers/baseline_policy.cc
diff --git a/sandbox/linux/seccomp-bpf-helpers/baseline_policy.cc b/sandbox/linux/seccomp-bpf-helpers/baseline_policy.cc
index 508ae3ebf91176592073a27cb5883c455ec053a1..79b5b023da4f07d429d18fe7a101c684ec7eb381 100644
--- a/sandbox/linux/seccomp-bpf-helpers/baseline_policy.cc
+++ b/sandbox/linux/seccomp-bpf-helpers/baseline_policy.cc
@@ -86,6 +86,13 @@ ErrorCode EvaluateSyscallImpl(int fs_denied_errno,
                               pid_t current_pid,
                               SandboxBPF* sandbox,
                               int sysno) {
+#if defined(ADDRESS_SANITIZER)
+  if (sysno == __NR_sigaltstack) {
+    // Required for better stack overflow detection in ASan. Disallowed in
+    // non-ASan builds.
+    return ErrorCode(ErrorCode::ERR_ALLOWED);
+  }
+#endif
   if (IsBaselinePolicyAllowed(sysno)) {
     return ErrorCode(ErrorCode::ERR_ALLOWED);
   }