Small debuggerd improvements.

Include the ABI in seccomp causes.

Slightly improved command-line usage information.

Fix crasher for seccomp failures.

Bug: N/A
Test: crasher
Change-Id: Ie419ecfe72ee4f5ccf49c927be18350a58a66a90
diff --git a/debuggerd/libdebuggerd/tombstone.cpp b/debuggerd/libdebuggerd/tombstone.cpp
index 3166bfc..4686bfd 100644
--- a/debuggerd/libdebuggerd/tombstone.cpp
+++ b/debuggerd/libdebuggerd/tombstone.cpp
@@ -214,7 +214,8 @@
       cause = "call to kuser_cmpxchg64";
     }
   } else if (si.si_signo == SIGSYS && si.si_code == SYS_SECCOMP) {
-    cause = StringPrintf("seccomp prevented call to disallowed system call %d", si.si_syscall);
+    cause = StringPrintf("seccomp prevented call to disallowed %s system call %d",
+                         ABI_STRING, si.si_syscall);
   }
 
   if (!cause.empty()) _LOG(log, logtype::HEADER, "Cause: %s\n", cause.c_str());