Qrack plugin: wrap CL_HPP version macros in ifndef

Signed-off-by: WrathfulSpatula <stranoj@gmail.com>

quantum/plugins/qrack/accelerator/QrackVisitor.hpp

@@ -18,8 +18,13 @@
 #include "AcceleratorBuffer.hpp"
 #include "OptionsProvider.hpp"
 
+#ifndef CL_HPP_TARGET_OPENCL_VERSION
 #define CL_HPP_TARGET_OPENCL_VERSION 200
+#endif
+
+#ifndef CL_HPP_MINIMUM_OPENCL_VERSION
 #define CL_HPP_MINIMUM_OPENCL_VERSION 100
+#endif
 
 #include "qrack/qfactory.hpp"