Skip tests if deps are not found.

test cases/csharp/4 external dep/meson.build

@@ -1,4 +1,9 @@
 project('C# external library', 'cs')
-glib_sharp_2 = dependency('glib-sharp-2.0')
+glib_sharp_2 = dependency('glib-sharp-2.0', required : false)
+
+if not glib_sharp_2.found()
+  error('MESON_SKIP_TEST glib# not found.')
+endif
+
 e = executable('prog', 'prog.cs', dependencies: glib_sharp_2, install : true)
 test('libtest', e, args: [join_paths(meson.current_source_dir(), 'hello.txt')])

test cases/csharp/4 pkgconfig/meson.build

@@ -1,6 +1,11 @@
 project('C# pkg-config', 'cs')
 
-nunit_dep = dependency('nunit')
+nunit_dep = dependency('nunit', required : false)
+
+if not nunit_dep.found()
+  error('MESON_SKIP_TEST nunit not found.')
+endif
+
 nunit_runner = find_program('nunit-console')
 
 test_lib = library('test_lib', 'test-lib.cs', dependencies: nunit_dep)