Updated GLFW to latest 3.4 (github master - 16Nov2020)

WARNING: Some CMake files not changed
WARNING: glfw_native.h contains custom changes

src/external/glfw/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.1)
+cmake_minimum_required(VERSION 3.1...3.17 FATAL_ERROR)
 
 project(GLFW VERSION 3.4.0 LANGUAGES C)
 
@@ -8,6 +8,10 @@ if (POLICY CMP0054)
     cmake_policy(SET CMP0054 NEW)
 endif()
 
+if (POLICY CMP0069)
+    cmake_policy(SET CMP0069 NEW)
+endif()
+
 if (POLICY CMP0077)
     cmake_policy(SET CMP0077 NEW)
 endif()
@@ -367,6 +371,11 @@ if (GLFW_INSTALL)
     install(FILES "${GLFW_BINARY_DIR}/src/glfw3.pc"
             DESTINATION "${CMAKE_INSTALL_LIBDIR}/pkgconfig")
 
+    if (DOXYGEN_FOUND AND GLFW_BUILD_DOCS)
+        install(DIRECTORY "${GLFW_BINARY_DIR}/docs/html"
+                DESTINATION "${CMAKE_INSTALL_DOCDIR}")
+    endif()
+
     # Only generate this target if no higher-level project already has
     if (NOT TARGET uninstall)
         configure_file(CMake/cmake_uninstall.cmake.in