[sysprof] build: only build libsysprof-ui if -Denable_gtk=true

[Christian Hergert <chergert src gnome org>]

commit 0d86933ed1b49d31352e1d387e0d1ee5e3332cbd
Author: Christian Hergert <chergert redhat com>
Date:   Mon Jun 3 12:19:45 2019 -0700

    build: only build libsysprof-ui if -Denable_gtk=true

 src/libsysprof-ui/meson.build | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/libsysprof-ui/meson.build b/src/libsysprof-ui/meson.build
index 37d8663..f25f5f2 100644
--- a/src/libsysprof-ui/meson.build
+++ b/src/libsysprof-ui/meson.build
@@ -1,3 +1,5 @@
+if get_option('enable_gtk')
+
 libsysprof_ui_public_sources = [
   'sysprof-aid.c',
   'sysprof-capture-view.c',
@@ -123,3 +125,5 @@ pkgconfig.generate(
 )
 
 install_headers(libsysprof_ui_public_headers, subdir: sysprof_header_subdir)
+
+endif