[SYCL] Remove std header inclusion from kernel_desc.hpp and use template proxy for int64_t (#6444)

Author: cperkinsintel

sycl/include/sycl/detail/kernel_desc.hpp

@@ -13,8 +13,6 @@
 #include <sycl/detail/defines_elementary.hpp>
 #include <sycl/detail/export.hpp>
 
-#include <cstdint>
-
 __SYCL_INLINE_NAMESPACE(cl) {
 namespace sycl {
 namespace detail {
@@ -23,6 +21,18 @@ namespace detail {
 #define _Bool bool
 #endif
 
+// As stated above, this header file cannot include any of the standard C++
+// headers. We need int64_t.  Here we are matching the exact definition used by
+// the SemaSYCL version of kernel_desc.hpp in the FE.
+template <bool Cond, typename TrueT, typename FalseT> struct conditional {
+  using type = TrueT;
+};
+template <typename TrueT, typename FalseT>
+struct conditional<false, TrueT, FalseT> {
+  using type = FalseT;
+};
+using int64_t = conditional<sizeof(long) == 8, long, long long>::type;
+
 // kernel parameter kinds
 enum class kernel_param_kind_t {
   kind_accessor = 0,