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.
CPPFLAGS, CFLAGS, CXXFLAGS and LDFLAGS are supposed to be under
user-control and putting configure-determined options in them broke
something as simple as running "make CXXFLAGS=-Wno-some-extra-warning"
because this overrode the CXXFLAGS set by configure and required for
build.
Improve this by using WX_*FLAGS in the generated makefile and leaving
the user-controlled FLAGS alone. This is still not ideal as running
"configure CFLAGS=-DFOO" and then "make CFLAGS=-DBAR" will define both
FOO and BAR, as configure copies CFLAGS to WX_CFLAGS, and so setting it
on make command line won't override it, as it should, but this should be
a much more rare and also much less severe problem, so we should be able
to live with it for now.
Normally this commit shouldn't result in any user-visible changes, i.e.
it shouldn't break any previously working scenarios and only make some
previously broken ones work.
Add a new class allowing to store passwords and other sensitive information
using the OS-provided facilities.
Add implementations for all the main platforms, documentation and a new sample
(which contains an ad hoc unit test as the real unit test for this class would
probably be a bad idea as it wouldn't run in non-interactive contexts and
could show OS level dialog boxes if it did).
