clover: Fix property_element::as for MSVC

MSVC doesn't like reinterpret_cast<T>(val) where neither T nor val
are pointers. It needs to be a static cast instead.

v2: Update assert to static_assert

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7680>

src/gallium/frontends/clover/core/property.hpp

@@ -199,12 +199,18 @@ namespace clover {
       }
 
       template<typename S>
-      S
+      typename std::enable_if<!std::is_convertible<T, S>::value, S>::type
       as() const {
-         assert(sizeof(S) <= sizeof(T));
+         static_assert(sizeof(S) <= sizeof(T), "Ensure type fits in property list");
          return reinterpret_cast<S>(x);
       }
 
+      template<typename S>
+      typename std::enable_if<std::is_convertible<T, S>::value, S>::type
+      as() const {
+         return static_cast<S>(x);
+      }
+
    private:
       T x;
    };