[Patch ObjC] fix objc.dg/exceptions2.m linkage error.

[Mike Stump]

On Dec 18, 2010, at 5:34 AM, Nicola Pero wrote:
> * it changes the compiler to emit the error "-fobjc-exceptions is required to enable Objective-C exception syntax"
> only once per compilation unit;
> 
> * it updates the ObjC testcases for this change;
> 
> * it adds corresponding ObjC++ testcases;
> 
> * it also changes the code to always call using_eh_for_cleanups() in objc_init(), if -fobjc-exceptions
> (but not -fobjc-sjlj-exceptions) is specified, without waiting for the first ObjC exception syntax (it
> makes more sense to me and it's the same way that the C++ frontend does it for C++ exceptions)
> 
> Ok to commit ?

Ok.  Please watch for regressions or build failures this time of year, given where we are in the release cycle.