Platform specific DMD tests

[Jacob Carlborg via Digitalmars-d]

I'm working on the D/Objective-C integration. There's a bunch of new 
tests added that should only be run on OS X. Currently these are in a 
separate test suite. How should these tests be handled? Should they stay 
in a separate test suite, exclude the files from the current makefile 
somehow or something else?

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/Jacob Carlborg