Math: work around missing std::round() in NaCl newlib.

Also test that our implementation behaves the same.

src/Math/Functions.h

@@ -251,12 +251,21 @@ template<std::size_t size, class T> Vector<size, T> floor(const Vector<size, T>&
 template<class T> inline T round(const T& a);
 #else
 template<class T> inline typename std::enable_if<std::is_arithmetic<T>::value, T>::type round(T a) {
+    #ifndef CORRADE_TARGET_NACL_NEWLIB
     return std::round(a);
+    #else
+    return (a > T(0)) ? std::floor(a + T(0.5)) : std::ceil(a - T(0.5));
+    #endif
 }
 template<std::size_t size, class T> Vector<size, T> round(const Vector<size, T>& a) {
     Vector<size, T> out;
-    for(std::size_t i = 0; i != size; ++i)
+    for(std::size_t i = 0; i != size; ++i) {
+        #ifndef CORRADE_TARGET_NACL_NEWLIB
         out[i] = std::round(a[i]);
+        #else
+        out[i] = round(a[i]);
+        #endif
+    }
     return out;
 }
 #endif

src/Math/Test/FunctionsTest.cpp

@@ -167,6 +167,15 @@ void FunctionsTest::floor() {
 void FunctionsTest::round() {
     CORRADE_COMPARE(Math::round(2.3f), 2.0f);
     CORRADE_COMPARE(Math::round(Vector3(2.3f, 0.7f, 1.5f)), Vector3(2.0f, 1.0f, 2.0f));
+
+    /* We are working around missing std::round() in NaCl newlib, thus we must
+       test that the behavior is the same on both implementations */
+    CORRADE_COMPARE(Math::round(-2.0f), -2.0f);
+    CORRADE_COMPARE(Math::round(-1.5f), -2.0f);
+    CORRADE_COMPARE(Math::round(-1.3f), -1.0f);
+    CORRADE_COMPARE(Math::round(1.3f), 1.0f);
+    CORRADE_COMPARE(Math::round(1.5f), 2.0f);
+    CORRADE_COMPARE(Math::round(2.0f), 2.0f);
 }
 
 void FunctionsTest::ceil() {