Fi: Building with FLTK_BUILD_GL=0 fails on systems without opengl ins…

…talled (fltk#1151)

test/CMakeLists.txt

@@ -245,11 +245,18 @@ if(CMAKE_CXX_COMPILER_ID IN_LIST _compilers)
   foreach(hd ${all_headers})
     get_filename_component(hd "${hd}" NAME)
     # skip headers that must not be included directly and fl_config.h if it exists
-    string(REGEX MATCH "^(mac|win32|x11|wayland|fl_config)\.[hH]$" skip "${hd}")
+    string(REGEX MATCH "^(mac|win32|x11|wayland|fl_config|gl[a-z_0-9]*)\.[hH]$" skip "${hd}")
     if(skip STREQUAL "")
       file(APPEND ${include_all} "#include <FL/${hd}>\n")
     endif()
   endforeach()
+  if(FLTK_USE_GL)
+    file(GLOB all_headers "${FLTK_SOURCE_DIR}/FL/gl*.[hH]")
+    foreach(hd ${all_headers})
+      get_filename_component(hd "${hd}" NAME)
+      file(APPEND ${include_all} "#include <FL/${hd}>\n")
+    endforeach()
+  endif(FLTK_USE_GL)
   file(APPEND ${include_all} "/* End of generated file */\n")
 
   # now add the 'shadow_variables' target and set the compiler flag