Do not use GL-related ifdefs for API-agnostic functionality.

src/Magnum/Magnum.h

@@ -204,18 +204,20 @@ Equivalent to GLSL @glsl int @ce.
 */
 typedef std::int32_t Int;
 
-#ifndef MAGNUM_TARGET_WEBGL
+#ifndef CORRADE_TARGET_EMSCRIPTEN
 /**
 @brief Unsigned long (64bit)
 
-@requires_gles 64-bit integers are not available in WebGL.
+@partialsupport 64-bit integers are not available under
+    @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten".
 */
 typedef std::uint64_t UnsignedLong;
 
 /**
 @brief Signed long (64bit)
 
-@requires_gles 64-bit integers are not available in WebGL.
+@partialsupport 64-bit integers are not available in
+    @ref CORRADE_TARGET_EMSCRIPTEN "Emscripten".
 */
 typedef std::int64_t Long;
 #endif

src/Magnum/Types.h

@@ -31,6 +31,7 @@
 
 #include <cstdint>
 
+#include "Corrade/configure.h"
 #include "Magnum/configure.h"
 
 namespace Magnum {
@@ -42,7 +43,7 @@ typedef std::uint16_t UnsignedShort;
 typedef std::int16_t Short;
 typedef std::uint32_t UnsignedInt;
 typedef std::int32_t Int;
-#ifndef MAGNUM_TARGET_WEBGL
+#ifndef CORRADE_TARGET_EMSCRIPTEN
 typedef std::uint64_t UnsignedLong;
 typedef std::int64_t Long;
 #endif