Add test to MatDense<FPP,GPU2>::mutliply.

misc/test/src/C++/test_matdense_gpu_mod.cpp.in

+#include "faust_constant.h"
+#include "faust_gpu_mod.h"
+#include "faust_MatDense_gpu.h"
+#include <cstdlib>
+using namespace Faust;
+
+int main(int argc, char** argv)
+{
+	faust_unsigned_int nrows = 10, ncols = 10;
+	faust_unsigned_int nrows2 = 10, ncols2 = 15;
+	double data[100];
+	Faust::enable_gpu_mod();
+	auto cpu_mat1 = Faust::MatDense<double,Cpu>::randMat(nrows,ncols);
+	MatDense<double,GPU2> gpu_mat1(cpu_mat1->getData(), nrows, ncols);
+	auto cpu_mat2 = Faust::MatDense<double,Cpu>::randMat(nrows2,ncols2);
+	MatDense<double,GPU2> gpu_mat2(cpu_mat2->getData(), nrows2, ncols2);
+	gpu_mat1.multiply(gpu_mat2);
+	auto cpu_mat1_mat2_test = gpu_mat2.tocpu();
+	auto cpu_mat1_mat2_ref = *cpu_mat2;
+	cpu_mat1->multiply(cpu_mat1_mat2_ref, 'N');
+	auto err_diff = cpu_mat1_mat2_ref;
+	err_diff -= cpu_mat1_mat2_test;
+	cout << "err mul." << err_diff.norm()/cpu_mat1_mat2_ref.norm() << endl;
+	return EXIT_SUCCESS;
+}