add msvc compatibility

srcs/FEM/my_code.cpp

+#ifdef _MSC_VER
+#include <gmsh.h_cwrap>       // gmsh main header
+#else
 #include <gmsh.h>       // gmsh main header
+#endif
+
 #include <iostream>     // for std::cout
 #include <map>
 #include <sstream>  // for std::stringstream
@@ -181,7 +186,13 @@ void Loop_K_F(const Eigen::Matrix<double, 3, 3> H_matrix, const double rho, cons
             double test1 = omp_get_wtime();
             //Eigen::setNbThreads(1);
             #pragma omp parallel for
+            #ifdef _MSC_VER
+            // https://github.com/tesseract-ocr/tesseract/issues/3285
+            // OpenMP 2.0 standard is enforced - we may use /openmp:llvm and keep size_t
+            for (int el = 0; el < elementTags[i].size(); el++){
+            #else
             for (std::size_t el = 0; el < elementTags[i].size(); el++){
+            #endif
                 // elemental K matrix and f vector initialization
                 Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic> K_matrix(2*numNodes,2*numNodes);
                 std::vector<double> f_vector(2*numNodes);