Convert the rule for libcxx so that it uses ARLIB_BUILD_CXX.
Convert the rule for libcxx so that it uses ARLIB_BUILD_CXX.

svn path=/trunk/; revision=3511

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot