Math: make the constructors in test also constexpr.

src/Magnum/Math/Test/MatrixTest.cpp

@@ -283,12 +283,12 @@ void MatrixTest::invertedOrthogonal() {
 
 template<class T> class BasicVec2: public Math::Vector<2, T> {
     public:
-        template<class ...U> BasicVec2(U&&... args): Math::Vector<2, T>{std::forward<U>(args)...} {}
+        template<class ...U> constexpr BasicVec2(U&&... args): Math::Vector<2, T>{std::forward<U>(args)...} {}
 };
 
 template<class T> class BasicMat2: public Math::Matrix<2, T> {
     public:
-        template<class ...U> BasicMat2(U&&... args): Math::Matrix<2, T>{std::forward<U>(args)...} {}
+        template<class ...U> constexpr BasicMat2(U&&... args): Math::Matrix<2, T>{std::forward<U>(args)...} {}
 
         MAGNUM_MATRIX_SUBCLASS_IMPLEMENTATION(2, BasicMat2, BasicVec2)
 };

src/Magnum/Math/Test/RectangularMatrixTest.cpp

@@ -413,7 +413,7 @@ void RectangularMatrixTest::vector() {
 
 template<std::size_t size, class T> class BasicMat: public Math::RectangularMatrix<size, size, T> {
     public:
-        template<class ...U> BasicMat(U&&... args): Math::RectangularMatrix<size, size, T>{std::forward<U>(args)...} {}
+        template<class ...U> constexpr BasicMat(U&&... args): Math::RectangularMatrix<size, size, T>{std::forward<U>(args)...} {}
 
         MAGNUM_RECTANGULARMATRIX_SUBCLASS_IMPLEMENTATION(size, size, BasicMat<size, T>)
 };
@@ -422,7 +422,7 @@ MAGNUM_MATRIX_OPERATOR_IMPLEMENTATION(BasicMat<size, T>)
 
 template<class T> class BasicMat2x2: public BasicMat<2, T> {
     public:
-        template<class ...U> BasicMat2x2(U&&... args): BasicMat<2, T>{std::forward<U>(args)...} {}
+        template<class ...U> constexpr BasicMat2x2(U&&... args): BasicMat<2, T>{std::forward<U>(args)...} {}
 
         MAGNUM_RECTANGULARMATRIX_SUBCLASS_IMPLEMENTATION(2, 2, BasicMat2x2<T>)
 };

src/Magnum/Math/Test/VectorTest.cpp

@@ -439,7 +439,7 @@ void VectorTest::angle() {
 
 template<class T> class BasicVec2: public Math::Vector<2, T> {
     public:
-        template<class ...U> BasicVec2(U&&... args): Math::Vector<2, T>{std::forward<U>(args)...} {}
+        template<class ...U> constexpr BasicVec2(U&&... args): Math::Vector<2, T>{std::forward<U>(args)...} {}
 
         MAGNUM_VECTOR_SUBCLASS_IMPLEMENTATION(2, BasicVec2)
 };