Fixed compilation errors on Windows

platforms/cpu/include/CpuGayBerneForce.h

@@ -42,7 +42,7 @@
 
 namespace OpenMM {
 
-class OPENMM_EXPORT CpuGayBerneForce {
+class CpuGayBerneForce {
 public:
     struct Matrix;
     class ComputeTask;

platforms/cpu/src/CpuGayBerneForce.cpp

@@ -29,11 +29,16 @@
  * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
  * -------------------------------------------------------------------------- */
 
+#ifdef _MSC_VER
+    // Prevent Windows from defining macros that interfere with other code.
+    #define NOMINMAX
+#endif
 #include "CpuGayBerneForce.h"
 #include "ReferenceForce.h"
 #include "openmm/OpenMMException.h"
 #include "openmm/GayBerneForce.h"
 #include "openmm/internal/gmx_atomic.h"
+#include <algorithm>
 #include <cmath>
 
 using namespace OpenMM;

platforms/reference/src/SimTKReference/ReferenceGayBerneForce.cpp

@@ -29,9 +29,14 @@
  * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
  * -------------------------------------------------------------------------- */
 
+#ifdef _MSC_VER
+    // Prevent Windows from defining macros that interfere with other code.
+    #define NOMINMAX
+#endif
 #include "ReferenceGayBerneForce.h"
 #include "ReferenceForce.h"
 #include "openmm/OpenMMException.h"
+#include <algorithm>
 #include <cmath>
 
 using namespace OpenMM;