build: separate version from the rest of the configuration data

This should make sure that we always have 'config.h' available and
should fix issues with flatpak build as seen in #257:

`fatal error: config.h: No such file or directory`

src/meson.build

@@ -109,20 +109,21 @@ calls_sources = files(['calls-message-source.c', 'calls-message-source.h',
                       ]) + wayland_sources + calls_generated_sources
 
 calls_config_data = config_data
-calls_config_data.set_quoted('VCS_TAG', '@VCS_TAG@')
 calls_config_data.set10('WL_SCANNER_FOUND', wl_scanner.found())
 
-config_h_in = configure_file(
-  output: 'config.h.in',
+config_h = configure_file(
+  output: 'config.h',
   configuration: calls_config_data
 )
 
-config_h = vcs_tag(
+version_h = vcs_tag(
     fallback: '',
-       input: config_h_in,
-      output: 'config.h',
+       input: 'version.h.in',
+      output: 'version.h',
 )
 
+calls_sources += [ version_h ]
+
 executable (
   'gnome-calls',
   calls_sources, 'main.c',