[mm-common] skeletonmm, Meson build: Use relative paths to untracked/

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 73aebe128f9e0aec6859df9c19002a19b39a9295
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Feb 25 14:22:51 2021 +0100

    skeletonmm, 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

 skeletonmm/skeleton/skeletonmm/meson.build | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/skeletonmm/skeleton/skeletonmm/meson.build b/skeletonmm/skeleton/skeletonmm/meson.build
index 6049cce..1c6409e 100644
--- a/skeletonmm/skeleton/skeletonmm/meson.build
+++ b/skeletonmm/skeleton/skeletonmm/meson.build
@@ -35,6 +35,7 @@ install_headers('..' / 'skeletonmm.h', subdir: skeletonmm_pcname)
 install_headers(extra_h_files, subdir: skeletonmm_pcname / 'skeletonmm')
 
 untracked_skeletonmm = 'untracked' / 'skeleton' / 'skeletonmm'
+rel_untracked_skeletonmm = '..' / '..' / untracked_skeletonmm
 src_untracked_skeletonmm = project_source_root / untracked_skeletonmm
 
 if maintainer_mode
@@ -129,9 +130,9 @@ else # not maintainer_mode
     hg_ccg_basenames,
   )
 
-  built_cc_files = [ src_untracked_skeletonmm / 'wrap_init.cc' ]
+  built_cc_files = [ rel_untracked_skeletonmm / 'wrap_init.cc' ]
   foreach file : hg_ccg_basenames
-    built_cc_files += src_untracked_skeletonmm / file + '.cc'
+    built_cc_files += rel_untracked_skeletonmm / file + '.cc'
   endforeach
 
   extra_include_dirs = [ '..', '..' / '..' / 'untracked' / 'skeleton' ]