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

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 091e801b2531c9e1cb8ec8064cca0d0d815e0c07
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Feb 25 10:02:22 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

 pango/pangomm/meson.build | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/pango/pangomm/meson.build b/pango/pangomm/meson.build
index 7523dcc..0910d2d 100644
--- a/pango/pangomm/meson.build
+++ b/pango/pangomm/meson.build
@@ -63,6 +63,7 @@ install_headers('..' / 'pangomm.h', subdir: pangomm_pcname)
 install_headers(extra_h_files, subdir: pangomm_pcname / 'pangomm')
 
 untracked_pangomm = 'untracked' / 'pango' / 'pangomm'
+rel_untracked_pangomm = '..' / '..' / untracked_pangomm
 src_untracked_pangomm = project_source_root / untracked_pangomm
 
 pangomm_cpp_args = [ '-DPANGOMM_BUILD=1' ]
@@ -190,9 +191,9 @@ else # not maintainer_mode
     hg_ccg_basenames,
   )
 
-  built_cc_files = [ src_untracked_pangomm / 'wrap_init.cc' ]
+  built_cc_files = [ rel_untracked_pangomm / 'wrap_init.cc' ]
   foreach file : hg_ccg_basenames
-    built_cc_files += src_untracked_pangomm / file + '.cc'
+    built_cc_files += rel_untracked_pangomm / file + '.cc'
   endforeach
 
   extra_include_dirs = [ '..', '..' / '..' / 'untracked' / 'pango' ]