* fix issue #3683 - fix ICU build on Linux
The following changes allow ICU to build on Linux:
- use the ICU tgz distribution rather than the zip file, to avoid CRLF
line endings on Linux
- don't use MSYS on Linux
- fix runConfigureICU options for Linux
- fix CFLAGS, CXXFLAGS, and LDFLAGS for Linux
- don't rename the resulting libraries on Linux
* [icu] Enable VCPKG_CXX_FLAGS
* [icu] Formatting
* Add doxygen to acquired programs
* Add packages option to msys function
* Add documentation for PACKAGES in vcpkg_require_msys
* [ffmpeg][x264] Update to use `PACKAGES` parameter. Tweak docs.