[beast/ebeast] BUILD: ensure MOSTLYCLEANFILES can be used with +=

[Tim Janik <timj src gnome org>]

commit a8dddd6fdc7336826e18491596a504cbbd24bffd
Author: Tim Janik <timj gnu org>
Date:   Mon Feb 27 14:43:09 2017 +0100

    BUILD: ensure MOSTLYCLEANFILES can be used with +=
    
    Signed-off-by: Tim Janik <timj gnu org>

 Makefile.decl |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/Makefile.decl b/Makefile.decl
index 2e24be0..1a7aa3e 100644
--- a/Makefile.decl
+++ b/Makefile.decl
@@ -4,6 +4,7 @@
 EXTRA_HEADERS=
 MAINTAINERCLEANFILES=$(GENERATED)
 CLEANFILES=$(GENERATED_CLEANFILES)
+MOSTLYCLEANFILES=
 GENERATED_EXTRA_DIST=
 GENERATED_CLEANFILES=
 GENERATED=$(strip $(GENERATED_EXTRA_DIST) $(GENERATED_CLEANFILES))