Put linker flags determined by configure after -L$(LIBDIRNAME) option
pointing to the directory containing the libraries being built, to
ensure that we link with these libraries rather than any wx libraries
globally installed in the system, as could be the case since the changes
of ec091c9f2b (Don't override CFLAGS etc in configure-generated
makefile, 2020-02-02).
See #18729.
47d881b683