Oh, std::pair is not constexpr in C++11.

That's why.

This partially reverts commit 628201946b.

src/Magnum/Test/VersionTest.cpp

@@ -75,11 +75,9 @@ void VersionTest::fromNumber() {
 
 void VersionTest::toNumber() {
     #ifndef MAGNUM_TARGET_GLES
-    constexpr const auto v = version(Version::GL430);
-    CORRADE_COMPARE(v, std::make_pair(4, 3));
+    CORRADE_COMPARE(version(Version::GL430), std::make_pair(4, 3));
     #else
-    constexpr const auto v = version(Version::GLES300);
-    CORRADE_COMPARE(v, std::make_pair(3, 0));
+    CORRADE_COMPARE(version(Version::GLES300), std::make_pair(3, 0));
     #endif
 }
 

src/Magnum/Version.h

@@ -118,9 +118,9 @@ constexpr Version version(Int major, Int minor) {
 
 @see @ref isVersionES()
 */
-constexpr std::pair<Int, Int> version(Version version) {
-    return {(Int(version) & ~Implementation::VersionESMask)/100,
-           ((Int(version) & ~Implementation::VersionESMask)%100)/10};
+inline std::pair<Int, Int> version(Version version) {
+    const Int v = Int(version) & ~Implementation::VersionESMask;
+    return {v/100, (v%100)/10};
 }
 
 /**