[gtk] docs: Fix references to pkg-config files

[Emmanuele Bassi <ebassi src gnome org>]

commit 22f073b57b2553f4259a1847d22ec827fea373fd
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Feb 6 10:40:51 2019 +0100

    docs: Fix references to pkg-config files
    
    The pkg-config files for GDK were dropped in 4.0, and now the GTK
    pkg-config files have been renamed.

 gdk/wayland/gdkdisplay-wayland.c | 3 +--
 gdk/x11/gdkmain-x11.c            | 3 +--
 2 files changed, 2 insertions(+), 4 deletions(-)
---
diff --git a/gdk/wayland/gdkdisplay-wayland.c b/gdk/wayland/gdkdisplay-wayland.c
index e6609559af..777b90b7ef 100644
--- a/gdk/wayland/gdkdisplay-wayland.c
+++ b/gdk/wayland/gdkdisplay-wayland.c
@@ -64,8 +64,7 @@
  *
  * The functions in this section are specific to the GDK Wayland backend.
  * To use them, you need to include the `<gdk/gdkwayland.h>` header and use
- * the Wayland-specific pkg-config files to build your application (either
- * `gdk-wayland-3.0` or `gtk+-wayland-3.0`).
+ * the Wayland-specific pkg-config `gtk4-wayland` file to build your application.
  *
  * To make your code compile with other GDK backends, guard backend-specific
  * calls by an ifdef as follows. Since GDK may be built with multiple
diff --git a/gdk/x11/gdkmain-x11.c b/gdk/x11/gdkmain-x11.c
index 4fe1d36b19..cce0cbb7d8 100644
--- a/gdk/x11/gdkmain-x11.c
+++ b/gdk/x11/gdkmain-x11.c
@@ -53,8 +53,7 @@
  *
  * The functions in this section are specific to the GDK X11 backend.
  * To use them, you need to include the `<gdk/gdkx.h>` header and use
- * the X11-specific pkg-config files to build your application (either
- * `gdk-x11-3.0` or `gtk+-x11-3.0`).
+ * the X11-specific pkg-config file `gtk4-x11` to build your application.
  *
  * To make your code compile with other GDK backends, guard backend-specific
  * calls by an ifdef as follows. Since GDK may be built with multiple