Add a test that uses hand-written vapi files

To use these, you just need to add the .vapi file to your target as
a source.

This test specifically tests that hand-written vapis referring to
C headers work.

test cases/vala/15 static vapi in source tree/meson.build

@@ -0,0 +1,13 @@
+project('static vapi', 'c', 'vala')
+
+glib = dependency('glib-2.0')
+
+conf = configuration_data()
+conf.set_quoted('VERSION', '1.0.0')
+config_h = configure_file(output : 'config.h',
+  configuration : conf)
+
+e = executable('static-vapi', 'vapi/config.vapi', 'test.vala',
+  dependencies : glib)
+
+test('test-config', e)

test cases/vala/15 static vapi in source tree/test.vala

@@ -0,0 +1,6 @@
+using GLib;
+using Config;
+
+public int main (string[] args) {
+  return GLib.strcmp(VERSION, "1.0.0");
+}

test cases/vala/15 static vapi in source tree/vapi/config.vapi

@@ -0,0 +1,4 @@
+[CCode (cprefix = "", lower_case_cprefix = "", cheader_filename = "config.h")]
+namespace Config {
+  public const string VERSION;
+}