<rdar://problem/6635688> Move HAVE_DTRACE check to Base.xcconfig

    <rdar://problem/6635688> Move HAVE_DTRACE check to Base.xcconfig

        Reviewed by Mark Rowe.

        * Configurations/Base.xcconfig: Set HAVE_DTRACE Xcode variable
        based on PLATFORM_NAME and MAC_OS_X_VERSION_MAJOR.  Also define
        it as a preprocessor macro by modifying
        GCC_PREPROCESSOR_DEFINITIONS.
        * JavaScriptCore.xcodeproj/project.pbxproj: Changed "Generate
        DTrace header" script phase to check for HAVE_DTRACE instead of
        MACOSX_DEPLOYMENT_TARGET.
        * wtf/Platform.h: Removed definition of HAVE_DTRACE macro since
        it's defined in Base.xcconfig now.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@41350 268f45cc-cd09-0410-ab3c-d52691b4dbfc