Use CXXFLAGS in the makefile's link rule since it invokes the C++
compiler front-end. Retool the makefile not to require GNU Make. Using
backticks instead of $(shell ...) is safe so long as one guards against
the possibility of backslashes getting inside the backticks, so use
temporary files and shell variables to avoid them.
Instead of relying on that some development package is installed on the
system, now a tiny library is built, which is the searched and used
during the test.
Alex