[atkmm] Meson build: Use relative paths to untracked/

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 2eac4d1e87de0b92088f8a08d3f1dd781cbf42af
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Feb 25 09:17:33 2021 +0100

    Meson build: Use relative paths to untracked/
    
    The paths to the source code in untracked/ shall be relative to the
    meson.build file, when library files are built from a tarball.
    With absolute paths Meson may generate too long file names.
    See merge request gtkmm!61

 atk/atkmm/meson.build | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/atk/atkmm/meson.build b/atk/atkmm/meson.build
index cb3db32..d39fc4a 100644
--- a/atk/atkmm/meson.build
+++ b/atk/atkmm/meson.build
@@ -58,6 +58,7 @@ install_headers('..' / 'atkmm.h', subdir: atkmm_pcname)
 install_headers(extra_h_files, subdir: atkmm_pcname / 'atkmm')
 
 untracked_atkmm = 'untracked' / 'atk' / 'atkmm'
+rel_untracked_atkmm = '..' / '..' / untracked_atkmm
 src_untracked_atkmm = project_source_root / untracked_atkmm
 
 atkmm_cpp_args = [ '-DATKMM_BUILD=1' ]
@@ -185,9 +186,9 @@ else # not maintainer_mode
     hg_ccg_basenames,
   )
 
-  built_cc_files = [ src_untracked_atkmm / 'wrap_init.cc' ]
+  built_cc_files = [ rel_untracked_atkmm / 'wrap_init.cc' ]
   foreach file : hg_ccg_basenames
-    built_cc_files += src_untracked_atkmm / file + '.cc'
+    built_cc_files += rel_untracked_atkmm / file + '.cc'
   endforeach
 
   extra_include_dirs = [ '..', '..' / '..' / 'untracked' / 'atk' ]