CMake: do not search for OpenGL library when DILIGENT_NO_OPENGL is set

Author: TheMostDiligent

CMakeLists.txt

@@ -470,9 +470,11 @@ elseif (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
 endif()
 
 if(PLATFORM_LINUX)
-    find_library(OPENGL_LIBRARY GL)
-    if (NOT OPENGL_LIBRARY)
-        message(FATAL_ERROR "Failed to find OpenGL library")
+    if(NOT DILIGENT_NO_OPENGL)
+        find_library(OPENGL_LIBRARY GL)
+        if (NOT OPENGL_LIBRARY)
+            message(FATAL_ERROR "Failed to find OpenGL library")
+        endif()
     endif()
 elseif(PLATFORM_MACOS)
     find_library(APP_KIT AppKit)