Math: fix/workaround constexpr test compilation on MSVC 2015.

src/Magnum/Math/Test/RectangularMatrixTest.cpp

@@ -600,12 +600,18 @@ void RectangularMatrixTest::subclass() {
     CORRADE_COMPARE(i*j, (BasicMat<1, Float>(6.0f)));
 
     /* Functions */
-    constexpr Mat2x2 flippedCols = Mat2x2{Vector2{-1.0f,  5.0f},
-                                          Vector2{ 7.0f, -2.0f}}.flippedCols();
+    #ifndef CORRADE_MSVC2015_COMPATIBILITY /* Probably because copy is not constexpr */
+    constexpr
+    #endif
+    Mat2x2 flippedCols = Mat2x2{Vector2{-1.0f,  5.0f},
+                                Vector2{ 7.0f, -2.0f}}.flippedCols();
     CORRADE_COMPARE(flippedCols, (Mat2x2{Vector2{ 7.0f, -2.0f},
                                          Vector2{-1.0f,  5.0f}}));
-    constexpr Mat2x2 flippedRows = Mat2x2{Vector2{-1.0f,  5.0f},
-                                          Vector2{ 7.0f, -2.0f}}.flippedRows();
+    #ifndef CORRADE_MSVC2015_COMPATIBILITY /* Probably because copy is not constexpr */
+    constexpr
+    #endif
+    Mat2x2 flippedRows = Mat2x2{Vector2{-1.0f,  5.0f},
+                                Vector2{ 7.0f, -2.0f}}.flippedRows();
     CORRADE_COMPARE(flippedRows, (Mat2x2{Vector2{ 5.0f, -1.0f},
                                          Vector2{-2.0f,  7.0f}}));
 }

src/Magnum/Math/Test/VectorTest.cpp

@@ -649,7 +649,10 @@ void VectorTest::subclass() {
     CORRADE_COMPARE(Vec2(3.0f, 0.0f).resized(6.0f), Vec2(6.0f, 0.0f));
     CORRADE_COMPARE(Vec2(1.0f, 1.0f).projected({0.0f, 2.0f}), Vec2(0.0f, 1.0f));
     CORRADE_COMPARE(Vec2(1.0f, 1.0f).projectedOntoNormalized({0.0f, 1.0f}), Vec2(0.0f, 1.0f));
-    constexpr Vec2 flipped = Vec2{1.0f, 0.4f}.flipped();
+    #ifndef CORRADE_MSVC2015_COMPATIBILITY /* Probably because copy is not constexpr */
+    constexpr
+    #endif
+    Vec2 flipped = Vec2{1.0f, 0.4f}.flipped();
     CORRADE_COMPARE(flipped, (Vec2{0.4f, 1.0f}));
 }