Meson: Add an option to skip tests for non-subproject builds

meson.build

@@ -18,7 +18,7 @@ dep_dxheaders = declare_dependency(
     link_with : guids_lib,
     include_directories : inc_dirs)
 
-if not meson.is_subproject()
+if not meson.is_subproject() and get_option('build-test')
     subdir('test')
 endif
 

meson_options.txt

@@ -0,0 +1,7 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+option('build-test',
+       type : 'boolean',
+       value : true,
+       description : 'Build the test')