ObjC/ObjC++: Move ObjC callbacks into their own header to fix pointless rebuilds of lots of files when they change

[Mike Stump]

On Dec 3, 2010, at 4:29 PM, Nicola Pero wrote:
> This patch fixes a problem I keep having when working on the Objective-C/Objective-C++
> frontends, which is that any, no-matter-how-trivial, change to the ObjC callbacks
> triggers a rebuild of a mass of completely unrelated files (such as i386.c,
> tree-ssa-mudflap.c, etc).

> Ok to commit ?

Ok.