[gobject-introspection] Meson: Fix build when gobject-introspection is a subproject

[Emmanuele Bassi <ebassi src gnome org>]

commit 0c414e34113fca089a67eb1beadfcdce722a89db
Author: Xavier Claessens <xavier claessens collabora com>
Date:   Thu Mar 25 16:39:52 2021 -0400

    Meson: Fix build when gobject-introspection is a subproject
    
    meson.source_root() return the root of the main project, but in this
    case we want the root of the gobject-introspection (sub)project.

 tests/offsets/meson.build | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/tests/offsets/meson.build b/tests/offsets/meson.build
index 71f4c8a4..f6a497f6 100644
--- a/tests/offsets/meson.build
+++ b/tests/offsets/meson.build
@@ -24,8 +24,8 @@ if glib_dep.type_name() == 'pkgconfig'
       '--output=@OUTPUT@',
       '--no-libtool',
       '--reparse-validate',
-      '--add-include-path', join_paths(meson.source_root(), 'gir'),
-      '--add-include-path', join_paths(meson.build_root(), 'gir'),
+      '--add-include-path', join_paths(source_root, 'gir'),
+      '--add-include-path', join_paths(build_root, 'gir'),
       '--warn-all',
       '--warn-error',
       '--namespace=Offsets',
@@ -34,7 +34,7 @@ if glib_dep.type_name() == 'pkgconfig'
       '--library=offsets-1.0',
       '-L', meson.current_build_dir(),
       '-I', meson.current_source_dir(),
-      '-I', join_paths(meson.source_root(), 'tests'),
+      '-I', join_paths(source_root, 'tests'),
       extra_giscanner_args,
       '@INPUT@',
     ]
@@ -46,7 +46,7 @@ if glib_dep.type_name() == 'pkgconfig'
     output: '@BASENAME@.typelib',
     depends: [gobject_gir, ],
     command: [gircompiler, '-o', '@OUTPUT@', '@INPUT@',
-              '--includedir', join_paths(meson.build_root(), 'gir'),
+              '--includedir', join_paths(build_root, 'gir'),
               '--includedir', meson.current_build_dir()
     ],
   )
@@ -58,10 +58,10 @@ if glib_dep.type_name() == 'pkgconfig'
   )
 
   test_offsets_env = environment()
-  test_offsets_env.set('top_builddir', join_paths(meson.build_root(), 'gir'))
+  test_offsets_env.set('top_builddir', join_paths(build_root, 'gir'))
   test_offsets_env.set('builddir', meson.current_build_dir())
   if host_system == 'windows'
-    test_offsets_env.prepend('PATH', join_paths(meson.build_root(), 'girepository'))
+    test_offsets_env.prepend('PATH', join_paths(build_root, 'girepository'))
   endif
 
   test('test_offsets.py',