Objective-C/C++: Ensure sufficient setup for the preprocessor.

Objective-C/C++: Ensure sufficient setup for the preprocessor.

The tokenizer makes use of functions that determine if identifiers
are interface or class names, and those functions need a hash map
to be set up.

This ensures that these are initialized before pre-process-only
jobs are run.

gcc/objc/ChangeLog:

	* objc-act.cc (objc_init): Initialize interface and class
	name hash maps before the preprocessor uses them.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
(cherry picked from commit 60f58d0630805e8dce79f5489658fd83e42fa8f1)