liblinear/Makefile should use CXXFLAGS from configure

[ryandesign]

liblinear/Makefile passes $(CFLAGS) to $(CXX). It should pass $(CXXFLAGS) instead. Further, it defines its own flags and does not use the ones the user specified in the environment variable when invoking ./configure. This causes the build to fail if the user has specified flags in CXXFLAGS that are required for the build to succeed. The MacPorts project's bug report about this problem is here: https://trac.macports.org/ticket/53995

[dmiller-nmap]

We will look into getting a temporary fix for this issue, but in the meantime please open an issue against cjlin1/liblinear as the upstream project.