Only look for OSMesa module if building examples

GLFW itself doesn't need the OSMesa headers to build.

CMakeLists.txt

@@ -260,13 +260,6 @@ if (_GLFW_WAYLAND)
     endif()
 endif()
 
-#--------------------------------------------------------------------
-# Use OSMesa for offscreen context creation
-#--------------------------------------------------------------------
-if (_GLFW_OSMESA)
-    find_package(OSMesa REQUIRED)
-endif()
-
 #--------------------------------------------------------------------
 # Use Cocoa for window creation and NSOpenGL for context creation
 #--------------------------------------------------------------------

examples/CMakeLists.txt

@@ -48,6 +48,7 @@ set_target_properties(${GUI_ONLY_BINARIES} ${CONSOLE_BINARIES} PROPERTIES
                       FOLDER "GLFW3/Examples")
 
 if (GLFW_USE_OSMESA)
+    find_package(OSMesa REQUIRED)
     target_compile_definitions(offscreen PRIVATE USE_NATIVE_OSMESA)
 endif()