render/egl: include EGL/eglmesaext.h only if present

This patch will make the EGL renderer work on any EGL/GLESv2 driver
providing the EGL_WL_bind_wayland_display extensions.

Mesa used to declare provisional EGL_WL_bind_wayland_display directly
in <EGL/eglext.h>. Then, all unofficial extensions were moved to
<EGL/eglmesaext.h>, to have a cleaner implementation. See:
ab7bb10a2a

The extension was then approved at Khronos Group, and reached the
official <EGL/eglext.h>. See:
https://www.khronos.org/registry/EGL/extensions/WL/EGL_WL_bind_wayland_display.txt
aa9b63f3ab

In order to make sure the renderer will work on any version of any
implementation providing the extension, only include the mesa-specific
header if it's present.

Signed-off-by: Julien Olivain <juju@cotds.org>

include/wlr/config.h.in

@@ -1,6 +1,8 @@
 #ifndef WLR_CONFIG_H
 #define WLR_CONFIG_H
 
+#mesondefine WLR_HAS_EGLMESAEXT_H
+
 #mesondefine WLR_HAS_LIBCAP
 
 #mesondefine WLR_HAS_SYSTEMD

include/wlr/render/egl.h

@@ -16,10 +16,14 @@
 #define EGL_NO_X11
 #endif
 
+#include <wlr/config.h>
+
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
+#if WLR_HAS_EGLMESAEXT_H
 // TODO: remove eglmesaext.h
 #include <EGL/eglmesaext.h>
+#endif
 #include <pixman.h>
 #include <stdbool.h>
 #include <wayland-server-core.h>

meson.build

@@ -86,6 +86,7 @@ conf_data.set10('WLR_HAS_X11_BACKEND', false)
 conf_data.set10('WLR_HAS_XWAYLAND', false)
 conf_data.set10('WLR_HAS_XCB_ERRORS', false)
 conf_data.set10('WLR_HAS_XCB_ICCCM', false)
+conf_data.set10('WLR_HAS_EGLMESAEXT_H', false)
 
 # Clang complains about some zeroed initializer lists (= {0}), even though they
 # are valid
@@ -109,6 +110,10 @@ pixman = dependency('pixman-1')
 math = cc.find_library('m')
 rt = cc.find_library('rt')
 
+if cc.has_header('EGL/eglmesaext.h', dependencies: egl)
+	conf_data.set10('WLR_HAS_EGLMESAEXT_H', true)
+endif
+
 wlr_files = []
 wlr_deps = [
 	wayland_server,