[gnome-system-monitor] Added atkmm dependency to fix build failure.

[Robert Roth <robertroth src gnome org>]

commit d7b5dae60928872509bb845a111dbc1518f64aa4
Author: Robert Roth <robert roth off gmail com>
Date:   Fri Jan 8 12:20:55 2021 +0200

    Added atkmm dependency to fix build failure.
    
    Theoretically gtkmm-3.0 should pull in atkmm, but it fails to do so.
    After consulting release team, it looks atkmm is also part of gnome-build-meta,
    so I am adding it as a dependency to be able to prepare the next release.

 meson.build     | 1 +
 src/meson.build | 1 +
 2 files changed, 2 insertions(+)
---
diff --git a/meson.build b/meson.build
index 19fa48d1..549b1aeb 100644
--- a/meson.build
+++ b/meson.build
@@ -46,6 +46,7 @@ glibmm  = dependency('glibmm-2.4',  version: '>=2.46')
 gmodule = dependency('gmodule-2.0')
 gtk3    = dependency('gtk+-3.0',    version: '>=3.22.0')
 gtkmm   = dependency('gtkmm-3.0',   version: '>=3.3.18')
+atkmm   = dependency('atkmm-1.6',   version: '>=2.28')
 libgtop = dependency('libgtop-2.0', version: '>=2.37.0')
 librsvg = dependency('librsvg-2.0', version: '>=2.35')
 libxml  = dependency('libxml-2.0',  version: '>=2.0')
diff --git a/src/meson.build b/src/meson.build
index 6669158a..3ff36b5f 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -95,6 +95,7 @@ executable(meson.project_name(),
   dependencies: [
     gmodule,
     gtkmm,
+    atkmm,
     libgtop,
     libsystemd,
     libwnck,