Makefile: Add support for local Makefile additions

With the recent addition of a check for directories listed in Makefile
local custom directories are always reported as unlisted. This patch
adds support for a “Makefile.local” file, which can adjust settings in
Makefile. Example: “DIRCHECK_EXCLUDE += xyz .mydata doc/manhtml”.
Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

.gitignore

@@ -12,6 +12,7 @@
 # /
 /Makefile
 /Makefile.in
+/Makefile.local
 /TAGS
 /aclocal.m4
 /autom4te.cache

Makefile.am

@@ -661,4 +661,6 @@ coverage: $(BUILT_SOURCES) $(python_tests)
 
 commit-check: distcheck lint apidoc
 
+-include ./Makefile.local
+
 # vim: set noet :