[SYCL] Reinclude spirv_vars in libdevice

Accidentally removed the inclusion of spirv_vars.hpp in device.h in 41ea7ab.
Reinclude it here.

Signed-off-by: Alexander Johnston <alexander@codeplay.com>

Author: Alexander Johnston

libdevice/device.h

@@ -6,6 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
+// We need the following header to ensure the definition of all spirv variables
+// required by the wrapper libraries.
+#include "spirv_vars.hpp"
+
 #ifndef __LIBDEVICE_DEVICE_H__
 #define __LIBDEVICE_DEVICE_H__