Enable CMake policy CMP0077 where available

This will let higher-level projects override GLFW CMake options with
normal variables instead of having to use cache variables.

This means with CMake 3.13 and later you can now do:

set(GLFW_BUILD_TESTS ON)
add_subdirectory(path/to/glfw)

Instead of the more verbose:

set(GLFW_BUILD_TESTS ON CACHE BOOL "" FORCE)
add_subdirectory(path/to/glfw)

(cherry picked from commit 71e6ff386d)

CMakeLists.txt

@@ -8,6 +8,10 @@ if (POLICY CMP0054)
     cmake_policy(SET CMP0054 NEW)
 endif()
 
+if (POLICY CMP0077)
+    cmake_policy(SET CMP0077 NEW)
+endif()
+
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
 option(BUILD_SHARED_LIBS "Build shared libraries" OFF)

README.md

@@ -220,6 +220,7 @@ skills.
  - Robin Leffmann
  - Glenn Lewis
  - Shane Liesegang
+ - Anders Lindqvist
  - Eyal Lotem
  - Aaron Loucks
  - Tristam MacDonald