* fix MSVC compiler shared library issues - mostly around 'extern const'
* add vcpkg install getopt to appveyor-windows.yml
show appveyor where to get getopt from vcpkg (non-static lib to avoid LGPL violation)
* add missing else case in lsquic_shared_support.h for windows static lib path
* have cmake spit out it's version
have cmake copy dependent dlls to build dir for tests on windows (getopt.dll)
* copy getopt.dll dep for tests
added commented version that requires >= 3.21 but handles any dll deps
* try caching boringssl dir to reduce CI build time since it's always same commit specified in config file
define VCPKG_ROOT in env since I can't seem to find it by VCPKG_ROOT or VCPKG_INSTALLED_DIR in appveyor's cmake v3.16 + vcpkg
* make windows cache dependent on yml and cmd
* sync up with changes to ls-qpack
George Wang
Tyler Young