From 2ab118a8591d8b27ae89de8f3c65b5797fd01dc2 Mon Sep 17 00:00:00 2001
From: Ben Boeckel <ben.boeckel@kitware.com>
Date: Mon, 20 Feb 2017 10:21:06 -0500
Subject: FindGTK2: handle old libsigc++ versions

Old versions of `libsigc++` do not have the version macros inside of its
`sigc++config.h` header. Assume nothing about such headers and report
version "zero".

Fixes: #16654
---
 Modules/FindGTK2.cmake | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Modules/FindGTK2.cmake b/Modules/FindGTK2.cmake
index 6747be5..20d7924 100644
--- a/Modules/FindGTK2.cmake
+++ b/Modules/FindGTK2.cmake
@@ -223,7 +223,10 @@ function(_GTK2_SIGCXX_GET_VERSION _OUT_major _OUT_minor _OUT_micro _sigcxxversio
         set(${_OUT_minor} ${${_OUT_minor}} PARENT_SCOPE)
         set(${_OUT_micro} ${${_OUT_micro}} PARENT_SCOPE)
     else()
-        message(FATAL_ERROR "Include file ${_gtkversion_hdr} does not exist")
+        # The header does not have the version macros; assume it is ``0.0.0``.
+        set(${_OUT_major} 0)
+        set(${_OUT_minor} 0)
+        set(${_OUT_micro} 0)
     endif()
 endfunction()
 
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