[devhelp] build: correctly remove generated file in distclean step

[Frederic Peters <fpeters src gnome org>]

commit 321170c6b90aecb98fe2fd00d5bb65f33568a2f9
Author: Frédéric Péters <fpeters 0d be>
Date:   Sun May 24 11:22:19 2015 +0200

    build: correctly remove generated file in distclean step

 src/Makefile.am |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/Makefile.am b/src/Makefile.am
index 94c319a..21651f1 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -114,3 +114,5 @@ dh-enum-types.h: dh-enum-types.h.template $(INST_H_FILES) $(GLIB_MKENUMS)
 
 dh-enum-types.c: dh-enum-types.c.template $(INST_H_FILES) $(GLIB_MKENUMS)
        $(AM_V_GEN) (cd $(srcdir) && $(GLIB_MKENUMS) --template dh-enum-types.c.template $(INST_H_FILES)) > $@
+
+DISTCLEANFILES = $(BUILT_SOURCES)