Fix sed script reading maint.mk.

[Ralf Wildenhues]

Hello all,

OK to apply?  Or would you rather have the $(srcdir)/ in $(ME)?

Thanks,
Ralf

    Fix sed script reading maint.mk.
    
    * top/maint.mk (MYSELF): New macro, define as $(srcdir)/$(ME).
    (syntax-check-rules): Use it.

diff --git a/top/maint.mk b/top/maint.mk
index 3756ee8..6d2ac03 100644
--- a/top/maint.mk
+++ b/top/maint.mk
@@ -18,6 +18,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 ME := maint.mk
+MYSELF := $(srcdir)/$(ME)
 
 # List of all C-like source code files that will be tested for
 # stylistic "errors".  You may want to define this to something
@@ -100,7 +101,7 @@ sc_changelog:
            exit 1; } || :
 
 # Collect the names of rules starting with `sc_'.
-syntax-check-rules := $(shell sed -n 's/^\(sc_[a-zA-Z0-9_-]*\):.*/\1/p' $(ME))
+syntax-check-rules := $(shell sed -n 's/^\(sc_[a-zA-Z0-9_-]*\):.*/\1/p' 
$(MYSELF))
 .PHONY: $(syntax-check-rules)
 
 syntax-check: $(syntax-check-rules)