Similar to other system libraries, use the builtin version on Windows and macOS
and try to find the system library on Unix.
Find the correct PCRE2 library based on the code point width that will be used.
Replace the use of Henry Spencer's regex library with PCRE at the build
level and enable wxUSE_PCRE in wxRegEx code to switch to PCRE-based
implementation there.
Note that this has to be done unconditionally because there is no simple
way to select between the previously used regex library and PCRE at the
makefiles level.
We could still keep the possibility to use the system regex library
under Unix, but this doesn't seem to be worth doing, as we don't support
Unicode REs properly when using it (and never did), so drop support for
this too.
Requires updates of expat and tiff submodules.
Most libraries have their own CMakeLists, add a comment with a suggestion to
use this for implementing build-in support.
Add CMake build system for libraries, tests and samples
update_files.py converts build/files into CMake format.
build/update-setup-h has been modified to update build/cmake/setup.h.in.
