cmake block(PROPAGATE) examples

microsoft/vcpkg ports/eigen3/portfile.cmake :3 

block(SCOPE_FOR VARIABLES PROPAGATE SOURCE_PATH)

microsoft/vcpkg ports/harfbuzz/portfile.cmake :69 

block(PROPAGATE cxx_link_libraries)

microsoft/vcpkg ports/openh264/portfile.cmake :12 

block(PROPAGATE cxx_link_libraries)

microsoft/vcpkg scripts/test_ports/vcpkg-ci-vcpkg-make/test-z_vcpkg_make_get_configure_triplets.cmake :16 

block(SCOPE_FOR VARIABLES  PROPAGATE build_opt)