[glibmm/glibmm-2-64] gmmproc: Fix compatibility with gtkmm 3.24.2

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 99e138ada3017dca1f8393ccf9072d1b14f9c910
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Fri Nov 27 13:10:18 2020 +0100

    gmmproc: Fix compatibility with gtkmm 3.24.2
    
    * tools/m4/class_shared.m4: Check if __FUNC_DECORATION__ is defined.
    class_gtkobject.m4 in gtkmm 3.24.2 and older does not define it.
    Fixes #82
    
    It's not necessary to push this patch to the master branch.
    That branch is not compatible with gtkmm-3 anyway.

 tools/m4/class_shared.m4 | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/tools/m4/class_shared.m4 b/tools/m4/class_shared.m4
index 587a1f2f..55f3250a 100644
--- a/tools/m4/class_shared.m4
+++ b/tools/m4/class_shared.m4
@@ -101,7 +101,12 @@ dnl
 dnl
 dnl
 define(`_PH_CLASS_DECLARATION',`dnl
+ifdef(`__FUNC_DECORATION__',`dnl
 class __FUNC_DECORATION__ __CPPNAME__`'_Class : public Glib::Class
+',`dnl
+dnl Old versions of class_gtkobject.m4 do not define __FUNC_DECORATION__.
+class __CPPNAME__`'_Class : public Glib::Class
+')dnl
 {
 public:
 #ifndef DOXYGEN_SHOULD_SKIP_THIS