package/weston: fix build with OpenGL ES disabled

package/weston: fix build with OpenGL ES disabled

Building this defconfig

BR2_TOOLCHAIN_BUILDROOT_LOCALE=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV=y
BR2_PACKAGE_MESA3D=y
BR2_PACKAGE_MESA3D_DRI_DRIVER_I965=y
BR2_PACKAGE_MESA3D_OPENGL_EGL=y
BR2_PACKAGE_WESTON=y
BR2_PACKAGE_XORG7=y

is broken:

  CC       clients/weston_simple_dmabuf_drm-simple-dmabuf-drm.o
clients/simple-dmabuf-drm.c: In function 'create_display':
clients/simple-dmabuf-drm.c:758:15: warning: implicit declaration of function 'eglQueryString' [-Wimplicit-function-declaration]
  extensions = eglQueryString(EGL_NO_DISPLAY, EGL_EXTENSIONS);
               ^~~~~~~~~~~~~~
clients/simple-dmabuf-drm.c:758:30: error: 'EGL_NO_DISPLAY' undeclared (first use in this function)
  extensions = eglQueryString(EGL_NO_DISPLAY, EGL_EXTENSIONS);
                              ^~~~~~~~~~~~~~
clients/simple-dmabuf-drm.c:758:30: note: each undeclared identifier is reported only once for each function it appears in
clients/simple-dmabuf-drm.c:758:46: error: 'EGL_EXTENSIONS' undeclared (first use in this function)
  extensions = eglQueryString(EGL_NO_DISPLAY, EGL_EXTENSIONS);
                                              ^~~~~~~~~~~~~~
clients/simple-dmabuf-drm.c:759:21: warning: implicit declaration of function 'weston_check_egl_extension' [-Wimplicit-function-declaration]
  if (extensions && !weston_check_egl_extension(extensions,

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>