[gtk-mac-integration] Mollify distcheck by dist-cleaning gtk-mac-integration.pc.

[John Ralls <jralls src gnome org>]

commit 5a924e5dd04a6bd02861faa8e2dd868447e9fcb5
Author: John Ralls <jralls ceridwen us>
Date:   Tue Sep 25 14:11:42 2018 -0700

    Mollify distcheck by dist-cleaning gtk-mac-integration.pc.

 data/Makefile.am | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/data/Makefile.am b/data/Makefile.am
index 7c3edd7..7935617 100644
--- a/data/Makefile.am
+++ b/data/Makefile.am
@@ -16,3 +16,5 @@ endif
 
 gtk-mac-integration.pc: ${default_pc_file}
        cp ${default_pc_file} $@
+
+DISTCLEANFILES=gtk-mac-integration.pc