GL: sigh, windows.h.

src/Magnum/GL/Renderer.cpp

@@ -368,6 +368,17 @@ void Renderer::setLogicOperation(const LogicOperation operation) {
 }
 #endif
 
+#if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
+/* https://docs.microsoft.com/en-us/windows/win32/api/winnt/nf-winnt-memorybarrier
+   Sigh. Our glMemoryBarrier is actually flextGL.MemoryBarrier and then
+   windows.h comes around and sets things on fire. Unless I'm doing something
+   very wrong, windows.h should not be dragged into this file, so no #undef
+   should be necessary. */
+void Renderer::setMemoryBarrier(MemoryBarriers barriers) {
+    glMemoryBarrier(GLbitfield(barriers));
+}
+#endif
+
 #ifndef MAGNUM_TARGET_WEBGL
 Renderer::ResetNotificationStrategy Renderer::resetNotificationStrategy() {
     #ifndef MAGNUM_TARGET_GLES

src/Magnum/GL/Renderer.h

@@ -1930,9 +1930,7 @@ class MAGNUM_GL_EXPORT Renderer {
          * @requires_gles31 Shader load/store is not available in OpenGL ES 3.0 and older.
          * @requires_gles Shader load/store is not available in WebGL.
          */
-        static void setMemoryBarrier(MemoryBarriers barriers) {
+        static void setMemoryBarrier(MemoryBarriers barriers);
-            glMemoryBarrier(GLbitfield(barriers));
-        }
 
         /**
          * @brief Set memory barrier by region