Made the version() functions constexpr.

Not sure why it wasn't like that before.

src/Magnum/Test/VersionTest.cpp

@@ -50,17 +50,21 @@ VersionTest::VersionTest() {
 
 void VersionTest::fromNumber() {
     #ifndef MAGNUM_TARGET_GLES
-    CORRADE_COMPARE(version(4, 3), Version::GL430);
+    constexpr const Version v = version(4, 3);
+    CORRADE_COMPARE(v, Version::GL430);
     #else
-    CORRADE_COMPARE(version(3, 0), Version::GLES300);
+    constexpr const Version v = version(3, 0);
+    CORRADE_COMPARE(v, Version::GLES300);
     #endif
 }
 
 void VersionTest::toNumber() {
     #ifndef MAGNUM_TARGET_GLES
-    CORRADE_COMPARE(version(Version::GL430), std::make_pair(4, 3));
+    constexpr const auto v = version(Version::GL430);
+    CORRADE_COMPARE(v, std::make_pair(4, 3));
     #else
-    CORRADE_COMPARE(version(Version::GLES300), std::make_pair(3, 0));
+    constexpr const auto v = version(Version::GLES300);
+    CORRADE_COMPARE(v, std::make_pair(3, 0));
     #endif
 }
 

src/Magnum/Version.h

@@ -100,12 +100,11 @@ enum class Version: Int {
 };
 
 /** @brief Enum value from major and minor version number */
-inline Version version(Int major, Int minor) {
+constexpr Version version(Int major, Int minor) {
     return Version(major*100 + minor*10);
 }
 
-/** @brief Major and minor version number from enum value */
+constexpr std::pair<Int, Int> version(Version version) {
-inline std::pair<Int, Int> version(Version version) {
     return {Int(version)/100, (Int(version)%100)/10};
 }