(TMPDIR): Make sure it's defined.

(my-distcheck): Build in $(TMPDIR), not `.'.

Makefile.maint

@@ -198,10 +198,11 @@ null_AM_MAKEFLAGS = \
 # by the use of _().  The --disable-nls effectively defines away that macro,
 # and building with CFLAGS='-Wformat -Werror' causes any format warning to be
 # treated as a failure.
-t=./=test
+TMPDIR ?= /tmp
+t=$(TMPDIR)/$(PACKAGE)/test
 my-distcheck: $(local-check)
 	-rm -rf $(t)
-	mkdir $(t)
+	mkdir -p $(t)
 	GZIP=$(GZIP_ENV) $(AMTAR) -C $(t) -zxf $(distdir).tar.gz
 	cd $(t)/$(distdir) \
 	  && ./configure --disable-nls \
@@ -210,8 +211,8 @@ my-distcheck: $(local-check)
 	  && $(MAKE) dvi \
 	  && $(MAKE) check \
 	  && $(MAKE) distclean
-	cd $(t) && mv $(distdir) $(distdir).old \
-	  && $(AMTAR) -zxf ../$(distdir).tar.gz
+	(cd $(t) && mv $(distdir) $(distdir).old \
+	  && $(AMTAR) -zxf - ) < $(distdir).tar.gz
 	diff -ur $(t)/$(distdir).old $(t)/$(distdir)
 	-rm -rf $(t)
 	@echo "========================"; \