Rename GlobalSynchronization to Locks

Also address some review comments in common_throws relating to
ToStr<InvokeType> and exception detail messages.

Change-Id: Ibf2c0f147689fa236d349bd7f01eed3c2522552b
diff --git a/src/runtime_linux.cc b/src/runtime_linux.cc
index 8365079..e503358 100644
--- a/src/runtime_linux.cc
+++ b/src/runtime_linux.cc
@@ -226,7 +226,7 @@
 };
 
 static void HandleUnexpectedSignal(int signal_number, siginfo_t* info, void* raw_context) {
-  MutexLock mu(*GlobalSynchronization::unexpected_signal_lock_);
+  MutexLock mu(*Locks::unexpected_signal_lock_);
 
   bool has_address = (signal_number == SIGILL || signal_number == SIGBUS ||
                       signal_number == SIGFPE || signal_number == SIGSEGV);