meson: only build imgui when needed

Only required for Intel tools or the Vulkan overlay layer.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
diff --git a/meson.build b/meson.build
index 9585807..e8bec9b 100644
--- a/meson.build
+++ b/meson.build
@@ -53,6 +53,7 @@
 with_glx_direct = get_option('glx-direct')
 with_osmesa = get_option('osmesa')
 with_swr_arches = get_option('swr-arches')
+with_vulkan_overlay_layer = get_option('vulkan-overlay-layer')
 with_tools = get_option('tools')
 if with_tools.contains('all')
   with_tools = [
@@ -69,6 +70,9 @@
   ]
 endif
 
+with_intel_tools = with_tools.contains('intel') or with_tools.contains('intel-ui')
+with_imgui = with_intel_tools or with_vulkan_overlay_layer
+
 dri_drivers_path = get_option('dri-drivers-path')
 if dri_drivers_path == ''
   dri_drivers_path = join_paths(get_option('prefix'), get_option('libdir'), 'dri')