GL: properly provide enum operators for Context::State.

doc/changelog.dox

@@ -68,6 +68,7 @@ See also:
 -   Don't assert in DPI scaling detection in @ref Platform::Sdl2Application and
     @ref Platform::GlfwApplication on X11 DEs that don't create any
     `RESOURCE_MANAGER` (see [mosra/magnum#290](https://github.com/mosra/magnum/issues/290))
+-   The @ref GL::Context::States enum set was missing value combining operators
 
 @subsection changelog-latest-docs Documentation
 

src/Magnum/GL/Context.h

@@ -692,6 +692,7 @@ class MAGNUM_GL_EXPORT Context {
 CORRADE_ENUMSET_OPERATORS(Context::Flags)
 #endif
 CORRADE_ENUMSET_OPERATORS(Context::DetectedDrivers)
+CORRADE_ENUMSET_OPERATORS(Context::States)
 
 #ifndef MAGNUM_TARGET_WEBGL
 /** @debugoperatorclassenum{Context,Context::Flag} */