Configure-based build: control presence of GL-related packages

configure.ac

@@ -1044,9 +1044,11 @@ AS_CASE([$host_os_gui], [cygwin* | mingw*], [
 
       AS_IF([test x$enable_gl != xno], [
           AS_IF([$PKGCONFIG --exists gl], [
+            AS_IF([$PKGCONFIG --exists egl], [
+              AS_IF([$PKGCONFIG --exists wayland-egl], [
                 AC_DEFINE([HAVE_GL])
                 GLLIBS="$($PKGCONFIG --libs wayland-egl) $($PKGCONFIG --libs egl) $($PKGCONFIG --libs gl) $GLLIBS"
-          ])
+          ])])])
           AS_IF([$PKGCONFIG --exists glu], [
              AC_DEFINE([HAVE_GL_GLU_H])
              GLLIBS="$($PKGCONFIG --libs glu) $GLLIBS"

src/drivers/Wayland/fl_wayland_gl_platform_init.cxx

@@ -14,6 +14,8 @@
 //     https://www.fltk.org/bugs.php
 //
 
+#include <config.h>
+#if HAVE_GL
 
 #include "Fl_Wayland_Gl_Window_Driver.H"
 #include "Fl_Wayland_Screen_Driver.H"
@@ -30,3 +32,5 @@ Fl_Gl_Window_Driver *Fl_Gl_Window_Driver::newGlWindowDriver(Fl_Gl_Window *w)
   return new Fl_Wayland_Gl_Window_Driver(w);
 #endif
 }
+
+#endif // HAVE_GL