gtkdoc: Run gtkdoc-scangobj command from build directory

All paths in CFLAGS are relative to build_root, so current directory
must be there we invoking gtkdoc-scangobj.

Closes: #3379

mesonbuild/modules/gnome.py

@@ -870,6 +870,8 @@ This will become a hard error in the future.''')
         for i in new_args:
             if expend_file_state and isinstance(i, mesonlib.File):
                 i = i.absolute_path(expend_file_state.environment.get_source_dir(), expend_file_state.environment.get_build_dir())
+            elif expend_file_state and isinstance(i, str):
+                i = os.path.join(expend_file_state.environment.get_source_dir(), expend_file_state.subdir, i)
             elif not isinstance(i, str):
                 raise MesonException(kwarg_name + ' values must be strings.')
             args.append(i)

mesonbuild/scripts/gtkdochelper.py

@@ -122,7 +122,8 @@ def build_gtkdoc(source_root, build_root, doc_subdir, src_subdirs,
                                                               '--module=' + module,
                                                               '--cflags=' + cflags,
                                                               '--ldflags=' + ldflags,
-                                                              '--ld=' + ld]
+                                                              '--ld=' + ld,
+                                                              '--output-dir=' + abs_out]
 
         library_paths = []
         for ldflag in shlex.split(ldflags):
@@ -132,7 +133,7 @@ def build_gtkdoc(source_root, build_root, doc_subdir, src_subdirs,
             library_paths.append(os.environ['LD_LIBRARY_PATH'])
         library_path = ':'.join(library_paths)
 
-        gtkdoc_run_check(scanobjs_cmd, abs_out, library_path)
+        gtkdoc_run_check(scanobjs_cmd, build_root, library_path)
 
     # Make docbook files
     if mode == 'auto':