clover/llvm: Use the highest supported SPIR-V version (v4)

clover/llvm: Use the highest supported SPIR-V version (v4)

v2:
   a) Move `supported_spirv_verssions()` to `spirv::` (Francisco Jerez)
   b) Introduce a `SPV_MAKE_VERSION` macro to avoid making mistakes and
     making it more readable than its uint representation.
v3: Replaced an if-statement with a `std::min()` in
    `spirv::get_spirv_translator_options()` (Karol Herbst)
v4: Turn `SPV_MAKE_VERSION()` into a function (Francisco Jerez)

Signed-off-by: Pierre Moreau <dev@pmoreau.org>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5038>