[libsoup/gnome-3-32] meson: fix the documentation src_dir value

[Claudio Saavedra <csaavedra src gnome org>]

commit 760ccac51825e1eca6703c3abd7eacbc2f17b634
Author: Claudio Saavedra <csaavedra igalia com>
Date:   Thu May 16 17:49:17 2019 +0300

    meson: fix the documentation src_dir value
    
    Use include_directories() instead of hardcoding it to make sure
    that both its source and build directory are included.

 docs/reference/meson.build | 2 +-
 meson.build                | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/docs/reference/meson.build b/docs/reference/meson.build
index 12105016..56d98686 100644
--- a/docs/reference/meson.build
+++ b/docs/reference/meson.build
@@ -55,7 +55,7 @@ scan_args = [
 
 gnome.gtkdoc('libsoup-2.4',
   main_sgml : 'libsoup-2.4-docs.sgml',
-  src_dir : join_paths(meson.source_root(), 'libsoup'),
+  src_dir : srcdir,
   ignore_headers : ignore_headers,
   mkdb_args : mkdb_args,
   scan_args : scan_args,
diff --git a/meson.build b/meson.build
index a212781b..6ff5a8e1 100644
--- a/meson.build
+++ b/meson.build
@@ -322,5 +322,6 @@ if get_option('tests')
  endif
 
 if get_option('gtk_doc')
+  srcdir = include_directories('libsoup')
   subdir('docs/reference')
 endif