Run the verifier single-threaded.

Also improve crash dumps so the frame numbers are the same as when you're
in gdb, and add a more memorably-named environment variable for waiting
for gdb.

(cherry picked from commit 5db7ea037e9acad434efe8ab4ce798c513fdb49a)

Change-Id: I428569d84dc5728bcd090919456395be44bdc97b
diff --git a/src/runtime_linux.cc b/src/runtime_linux.cc
index 5856f06..88a4a25 100644
--- a/src/runtime_linux.cc
+++ b/src/runtime_linux.cc
@@ -254,8 +254,7 @@
                       << "Registers:\n" << Dumpable<UContext>(thread_context) << "\n"
                       << "Backtrace:\n" << Dumpable<Backtrace>(thread_backtrace);
 
-  // TODO: instead, get debuggerd running on the host, try to connect, and hang around on success.
-  if (getenv("debug_db_uid") != NULL) {
+  if (getenv("debug_db_uid") != NULL || getenv("art_wait_for_gdb_on_crash") != NULL) {
     LOG(INTERNAL_FATAL) << "********************************************************\n"
                         << "* Process " << getpid() << " thread " << tid << " \"" << thread_name << "\""
                         << " has been suspended while crashing.\n"