Cocoa: Fix ObjC being built as C with CMake 3.19

CMake 3.19 adds -xc when the LANGUAGE file property is C, breaking our
workaround for CMake 3.15 and earlier not understanding the .m suffix.

Fixes #1787.

README.md

@@ -177,6 +177,7 @@ information on what to include when reporting a bug.
    (#1635)
  - [Cocoa] Bugfix: Failing to retrieve the refresh rate of built-in displays
    could leak memory
+ - [Cocoa] Bugfix: Objective-C files were compiled as C with CMake 3.19 (#1787)
  - [X11] Bugfix: The CMake files did not check for the XInput headers (#1480)
  - [X11] Bugfix: Key names were not updated when the keyboard layout changed
    (#1462,#1528)
@@ -322,6 +323,7 @@ skills.
  - Konstantin Käfer
  - Eric Larson
  - Francis Lecavalier
+ - Jong Won Lee
  - Robin Leffmann
  - Glenn Lewis
  - Shane Liesegang

src/CMakeLists.txt

@@ -112,7 +112,7 @@ target_include_directories(glfw PRIVATE
 target_link_libraries(glfw PRIVATE Threads::Threads ${glfw_LIBRARIES})
 
 # Workaround for CMake not knowing about .m files before version 3.16
-if (APPLE)
+if ("${CMAKE_VERSION}" VERSION_LESS "3.16" AND APPLE)
     set_source_files_properties(cocoa_init.m cocoa_joystick.m cocoa_monitor.m
                                 cocoa_window.m nsgl_context.m PROPERTIES
                                 LANGUAGE C)