cmake: add a preparatory work-around to accommodate `vcpkg`

We are about to add support for installing the `.dll` files of Git's dependencies (such as libcurl) in the CMake configuration. The `vcpkg` ecosystem from which we get said dependencies makes that relatively easy: simply turn on `X_VCPKG_APPLOCAL_DEPS_INSTALL`. However, current `vcpkg` introduces a limitation if one does that: While it is totally cool with CMake to specify multiple targets within one invocation of `install(TARGETS ...) (at least according to https://cmake.org/cmake/help/latest/command/install.html#command:install), `vcpkg`'s parser insists on a single target per `install(TARGETS ...)` invocation. Well, that's easily accomplished: Let's feed the targets individually to the `install(TARGETS ...)` function in a `foreach()` look. This also has the advantage that we do not have to manually cull off the two entries from the `${PROGRAMS_BUILT}` array before scheduling the remainder to be installed into `libexec/git-core`. Instead, we iterate through the array and decide for each entry where it wants to go. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>