glx: include: meson_options.txt: Allow disabling DRI glx backends

This allows building the X server with glx and without mesa.
This also makes the X server optionally no longer be a loader for dri drivers.

Fixes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1638
Fixes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1819

Signed-off-by: stefan11111 <stefan11111@shitposting.expert>

glx/glxext.c

@@ -272,7 +272,12 @@ glxClientCallback(CallbackListPtr *list, void *closure, void *data)
 
 /************************************************************************/
 
-static __GLXprovider *__glXProviderStack = &__glXDRISWRastProvider;
+static __GLXprovider *__glXProviderStack =
+#ifdef BUILD_GLX_DRI
+                                           &__glXDRISWRastProvider;
+#else
+                                           NULL;
+#endif
 
 void
 GlxPushProvider(__GLXprovider * provider)

glx/meson.build

@@ -13,8 +13,6 @@ srcs_glx = [
     'glxcmds.c',
     'glxcmdsswap.c',
     'glxext.c',
-    'glxdriswrast.c',
-    'glxdricommon.c',
     'glxscreens.c',
     'render2.c',
     'render2swap.c',
@@ -30,6 +28,16 @@ srcs_glx = [
     'xfont.c',
 ]
 
+srcs_glxdri2 = []
+if build_glx_dri
+    srcs_glx += 'glx_dri/glxdriswrast.c'
+    srcs_glx += 'glx_dri/glxdricommon.c'
+
+    if build_dri2 or build_dri3
+        srcs_glxdri2 = files('glx_dri/glxdri2.c')
+    endif
+endif
+
 libxserver_glx = []
 if build_glx
     libxserver_glx = static_library('xserver_glx',
@@ -50,11 +58,6 @@ if build_glx
     )
 endif
 
-srcs_glxdri2 = []
-if build_dri2 or build_dri3
-    srcs_glxdri2 = files('glxdri2.c')
-endif
-
 srcs_vnd = [
     'vndcmds.c',
     'vndext.c',