[google/integration] Add placeholder flags for -Wthread-*

Introduce placeholder flags for thread annotation support.  This is
being implemented in the thread-annotations branch, but Google code
expects these warnings to be supported by the compiler.

Tested on x86_64.  Committed on google/integration.


2011-02-01  Diego Novillo  <dnovillo@google.com>

	* common.opt (Wthread-safe, Wthread-unguarded-var,
	Wthread-unguarded-func, Wthread-mismatched-lock-order,
	Wthread-mismatched-lock-acq-rel, Wthread-reentrant-lock,
	Wthread-unsupported-lock-name): New placeholder warning flags.

[simonb, 2011-02-02 16:16:03]

OK