toytoolkit: make all EGL code dependant on cairo-egl

configure.ac: The toytoolkit clients used to get libEGL linked to them
even if there was no cairo-egl. This is useless, and actually harmful on
platforms, where libEGL absolutely requires one of the GL ES libraries
to be linked in, too.

Look for EGL-related packages only for cairo-egl with toytoolkit.

window.c: protect all GL header includes with HAVE_CAIRO_EGL, since that
is the only case we can support EGL, GL, or GLESv2 at all. In the case
we do not have cairo-egl, add enough definitions to let us build the
stubs for EGL-related functions.

Remove some #ifdefs that were inside of the same #ifdef already.

These changes allow to build sorfware rendering toytoolkit clients
without any bits of EGL libs or headers.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/configure.ac b/configure.ac
index c2cd7da..8b8e9a2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -164,7 +164,7 @@
 if test x$enable_clients = xyes; then
   AC_DEFINE([BUILD_CLIENTS], [1], [Build the Wayland clients])
 
-  PKG_CHECK_MODULES(CLIENT, [wayland-client wayland-egl egl >= 7.10 cairo >= 1.10.0 xkbcommon wayland-cursor])
+  PKG_CHECK_MODULES(CLIENT, [wayland-client cairo >= 1.10.0 xkbcommon wayland-cursor])
   PKG_CHECK_MODULES(WESTON_INFO, [wayland-client])
 
   CLIENT_CFLAGS="$CLIENT_CFLAGS $IMAGE_CFLAGS"
@@ -172,7 +172,7 @@
 
   PKG_CHECK_MODULES(POPPLER, [poppler-glib glib-2.0 gobject-2.0 gio-2.0 ],
 			     [have_poppler=yes], [have_poppler=no])
-  PKG_CHECK_MODULES(CAIRO_EGL, [cairo-egl >= 1.11.3 $cairo_modules],
+  PKG_CHECK_MODULES(CAIRO_EGL, [wayland-egl egl >= 7.10 cairo-egl >= 1.11.3 $cairo_modules],
 		    [have_cairo_egl=yes], [have_cairo_egl=no])
   AS_IF([test "x$have_cairo_egl" = "xyes"],
         [AC_DEFINE([HAVE_CAIRO_EGL], [1], [Have cairo-egl])],