GCC 4.6 compatibility: can't list-initialize array of classes.

Awesome bug. In GCC 4.6 it throws plenty of ungoogleable `-pedantic`
warnings and in GCC 4.5 it fails directly with "error: bad array
initializer". Fallback to initialization using for-cycle.

Hello, performance? You can go home now.

src/Math/RectangularMatrix.h

@@ -106,7 +106,12 @@ template<std::size_t cols, std::size_t rows, class T> class RectangularMatrix {
          *
          * @todo Creating matrix from arbitrary combination of matrices with n rows
          */
+        #ifndef CORRADE_GCC46_COMPATIBILITY
         template<class ...U> inline constexpr /*implicit*/ RectangularMatrix(const Vector<rows, T>& first, const U&... next): _data{first, next...} {
+        #else
+        template<class ...U> inline /*implicit*/ RectangularMatrix(const Vector<rows, T>& first, const U&... next): _data() {
+            constructInternal({first, next...});
+        #endif
             static_assert(sizeof...(next)+1 == cols, "Improper number of arguments passed to RectangularMatrix constructor");
         }
 
@@ -443,7 +448,21 @@ template<std::size_t cols, std::size_t rows, class T> class RectangularMatrix {
 
     private:
         /* Implementation for RectangularMatrix<cols, rows, T>::RectangularMatrix(const RectangularMatrix<cols, rows, U>&) */
+        #ifndef CORRADE_GCC46_COMPATIBILITY
         template<class U, std::size_t ...sequence> inline constexpr explicit RectangularMatrix(Implementation::Sequence<sequence...>, const RectangularMatrix<cols, rows, U>& matrix): _data{Vector<rows, T>(matrix[sequence])...} {}
+        #else
+        template<class U, std::size_t ...sequence> inline constexpr explicit RectangularMatrix(Implementation::Sequence<sequence...>, const RectangularMatrix<cols, rows, U>& matrix): _data() {
+            constructInternal({Vector<rows, T>(matrix[sequence])...});
+        }
+        #endif
+
+        #ifdef CORRADE_GCC46_COMPATIBILITY
+        /* GCC < 4.7 workaround for a ton of warnings / "error: bad array initializer" */
+        inline void constructInternal(std::initializer_list<Vector<rows, T>> data) {
+            for(std::size_t i = 0; i != data.size(); ++i)
+                _data[i] = *(data.begin() + i);
+        }
+        #endif
 
         Vector<rows, T> _data[cols];
 };