RFR: JDK-8074099 Even with toolchain type clang, OBJC is set to gcc

[David DeHaven]

>> Open question: Should we do the same for toolchain-type=gcc? I'm not quite sure what we're getting from calling the AC_PROG_OBJC macro, except perhaps a loss of transparency on how our tools are picked up. :-/ In fact, maybe we should just skip the OBJC variable completely. In fact, for Objective-C++ (.mm) files, we just use the normal C++ compiler. 
> 
> The more I think of it, the more I like this idea. Here's a new patch that does exactly this.
> 
> WebRev: http://cr.openjdk.java.net/~ihse/JDK-8074099-remove-objc/webrev.01

That looks good to me.

-DrD-