Update minimum CMake version to 3.16

This replaces some workarounds and manual logic with new features
available with CMake 3.16, including list(FILTER), list(JOIN),
foreach(IN LISTS) and enable_language(OBJC).  Policy settings no longer
needed with 3.16 have been removed.

Related to #2541

src/CMakeLists.txt

@@ -30,6 +30,7 @@ add_custom_target(update_mappings
 set_target_properties(update_mappings PROPERTIES FOLDER "GLFW3")
 
 if (GLFW_BUILD_COCOA)
+    enable_language(OBJC)
     target_compile_definitions(glfw PRIVATE _GLFW_COCOA)
     target_sources(glfw PRIVATE cocoa_platform.h cocoa_joystick.h cocoa_init.m
                                 cocoa_joystick.m cocoa_monitor.m cocoa_window.m
@@ -137,13 +138,6 @@ target_include_directories(glfw PRIVATE
                            "${GLFW_BINARY_DIR}/src")
 target_link_libraries(glfw PRIVATE Threads::Threads)
 
-# Workaround for CMake not knowing about .m files before version 3.16
-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)
-endif()
-
 if (GLFW_BUILD_WIN32)
     list(APPEND glfw_PKG_LIBS "-lgdi32")
 endif()
@@ -349,12 +343,8 @@ if (GLFW_BUILD_SHARED_LIBRARY)
     endif()
 endif()
 
-foreach(arg ${glfw_PKG_DEPS})
-    string(APPEND deps " ${arg}")
-endforeach()
-foreach(arg ${glfw_PKG_LIBS})
-    string(APPEND libs " ${arg}")
-endforeach()
+list(JOIN glfw_PKG_DEPS " " deps)
+list(JOIN glfw_PKG_LIBS " " libs)
 
 set(GLFW_PKG_CONFIG_REQUIRES_PRIVATE "${deps}" CACHE INTERNAL
     "GLFW pkg-config Requires.private")