[pangomm] Meson build: Fix versioning on macOS

[Kjell Ahlstedt <kjellahl src gnome org>]

commit a9b06f665c912d1160d7ce380afecf88c2c2a3b9
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Thu Oct 1 10:15:24 2020 +0200

    Meson build: Fix versioning on macOS
    
    See libsigcplusplus, pull request 65

 meson.build               | 7 ++++++-
 pango/pangomm/meson.build | 2 ++
 2 files changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 71ad3b6..f19adc6 100644
--- a/meson.build
+++ b/meson.build
@@ -29,7 +29,12 @@ libtool_soversion = [1, 30, 0]
 pangomm_libversion = '@0@.@1@.@2@'.format(
   libtool_soversion[0] - libtool_soversion[2],
   libtool_soversion[2],
-  libtool_soversion[1])
+  libtool_soversion[1]
+)
+macos_darwin_versions = [
+  libtool_soversion[0] + 1,
+  '@0@.@1@'.format(libtool_soversion[0] + 1, libtool_soversion[1])
+]
 
 # Use these instead of meson.source_root() and meson.build_root() in subdirectories.
 # source_root() and build_root() are not useful, if this is a subproject.
diff --git a/pango/pangomm/meson.build b/pango/pangomm/meson.build
index f576421..7523dcc 100644
--- a/pango/pangomm/meson.build
+++ b/pango/pangomm/meson.build
@@ -156,6 +156,7 @@ if maintainer_mode
   pangomm_library = library(pangomm_libname, extra_pangomm_objects,
     built_cc_file_targets, extra_cc_files, built_dummy_h_file_target,
     version: pangomm_libversion,
+    darwin_versions: macos_darwin_versions,
     include_directories: extra_include_dirs,
     cpp_args: pangomm_cpp_args,
     dependencies: pangomm_build_dep,
@@ -199,6 +200,7 @@ else # not maintainer_mode
   pangomm_library = library(pangomm_libname, extra_pangomm_objects,
     built_cc_files, extra_cc_files,
     version: pangomm_libversion,
+    darwin_versions: macos_darwin_versions,
     include_directories: extra_include_dirs,
     cpp_args: pangomm_cpp_args,
     dependencies: pangomm_build_dep,