We don't need the UseEmscripten module for anything.

CMakeLists.txt

@@ -291,10 +291,6 @@ if(TARGET_VK)
     set(MAGNUM_TARGET_VK 1)
 endif()
 
-if(CORRADE_TARGET_EMSCRIPTEN)
-    include(UseEmscripten)
-endif()
-
 if(WITH_OPENGLTESTER)
     if(MAGNUM_TARGET_HEADLESS OR CORRADE_TARGET_EMSCRIPTEN OR CORRADE_TARGET_ANDROID)
         set(WITH_WINDOWLESSEGLAPPLICATION ON)

doc/changelog.dox

@@ -246,6 +246,8 @@ See also:
 -   Switched Emscripten build from macOS to Ubuntu + Docker for 2x faster build
     times (see [mosra/magnum#350](https://github.com/mosra/magnum/issues/350))
 -   Linux, Emscripten and macOS builds were migrated from Travis to Circle CI
+-   `UseEmscripten` is no longer implicitly included on Emscripten as it's not
+    needed for anything (see [mosra/magnum#490](https://github.com/mosra/magnum/issues/490))
 -   @ref Trade::ObjImporter "ObjImporter" uses exceptions internally and needs
     an explicit exception-enabling flag when built with Emscripten 1.39.0 and
     newer