When running CMake 3.21 or newer in trace or debug mode, vcpkg.cmake
would trigger the CMP0126 warning for VCPKG_MANIFEST_DIR and
VCPKG_INSTALLED_DIR.
The regular variable was used to set the initial value of the cache
variable of the same name. This patch adds the regular variables
Z_VCPKG_MANIFEST_DIR_INITIAL_VALUE and
Z_VCPKG_INSTALLED_DIR_INITIAL_VALUE that are used to initialize their
respective cache variables.
512d62f7ee