tests: more significant names for some tests * t/extra2.sh: Rename... * t/extra-sources-no-spurious.sh: ... like this. * t/yflags2.sh: Rename... * t/yflags-cxx.sh: ... like this. * t/lflags2.sh: Rename... * t/lflags-cxx.sh: ... like this. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>