Add EGL_NO_PLATFORM_SPECIFIC_TYPES to avoid Xlib.h via EGL headers

See: https://github.com/KhronosGroup/EGL-Registry/pull/111 discussion.

Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
diff --git a/meson.build b/meson.build
index cb1c6bb..749d17b 100644
--- a/meson.build
+++ b/meson.build
@@ -102,6 +102,7 @@
 config_h.set('_ALL_SOURCE', '1')
 config_h.set('EGL_NO_X11', '1')
 config_h.set('MESA_EGL_NO_X11_HEADERS', '1')
+config_h.set('EGL_NO_PLATFORM_SPECIFIC_TYPES', '1')
 
 config_h.set_quoted('PACKAGE_STRING', 'weston @0@'.format(version_weston))
 config_h.set_quoted('PACKAGE_VERSION', version_weston)