vala: Build with '--nostdpkg'

Since Vala require 'glib-2.0' and 'gobject-2.0' dependencies, it's
better to fail at 'valac' step with meaningful error.

Add missing 'gobject-2.0' dependency on the mixed source test case.

mesonbuild/backend/ninjabackend.py

@@ -1024,6 +1024,7 @@ int dummy;
         # found inside the build tree (generated sources).
         args += ['-d', c_out_dir]
         args += ['-C']
+        args += ['--nostdpkg']
         if not isinstance(target, build.Executable):
             # Library name
             args += ['--library=' + target.name]

test cases/vala/11 mixed sources/meson.build

@@ -1,7 +1,8 @@
 project('foo', 'c', 'vala')
 
 glib = dependency('glib-2.0')
+gobject = dependency('gobject-2.0')
 
 subdir('c')
-e = executable('foo', 'c/foo.c', retval, 'vala/bar.vala', dependencies: [glib])
+e = executable('foo', 'c/foo.c', retval, 'vala/bar.vala', dependencies: [glib, gobject])
 test('test foo', e)