Eliminated compilation errors on devices that don't support 64 bit integers

platforms/opencl/src/OpenCLContext.cpp

@@ -277,6 +277,7 @@ OpenCLContext::OpenCLContext(const System& system, int platformIndex, int device
     clearFiveBuffersKernel = cl::Kernel(utilities, "clearFiveBuffers");
     clearSixBuffersKernel = cl::Kernel(utilities, "clearSixBuffers");
     reduceReal4Kernel = cl::Kernel(utilities, "reduceReal4Buffer");
+    if (supports64BitGlobalAtomics)
         reduceForcesKernel = cl::Kernel(utilities, "reduceForces");
 
     // Decide whether native_sqrt(), native_rsqrt(), and native_recip() are sufficiently accurate to use.

platforms/opencl/src/kernels/utilities.cl

@@ -81,6 +81,7 @@ __kernel void reduceReal4Buffer(__global real4* restrict buffer, int bufferSize,
     }
 }
 
+#ifdef SUPPORTS_64_BIT_ATOMICS
 /**
  * Sum the various buffers containing forces.
  */
@@ -94,6 +95,7 @@ __kernel void reduceForces(__global const long* restrict longBuffer, __global re
         buffer[index] = sum;
     }
 }
+#endif
 
 /**
  * This is called to determine the accuracy of various native functions.