Avoid the use of the -u option with mktemp.

Makefile.in

@@ -227,8 +227,8 @@ zlib.3.pdf: zlib.3
 	groff -mandoc -f H -T ps zlib.3 | ps2pdf - zlib.3.pdf
 
 zconf.h.cmakein: zconf.h.in
-	-@ TEMPFILE=`mktemp -u __XXXXXX`; \
-	echo "/#define ZCONF_H/ a\\\\\n#cmakedefine Z_PREFIX\\\\\n#cmakedefine Z_HAVE_UNISTD_H\n" > $$TEMPFILE &&\
+	-@ TEMPFILE=`mktemp __XXXXXX`; \
+	echo "/#define ZCONF_H/ a\\\\\n#cmakedefine Z_PREFIX\\\\\n#cmakedefine Z_HAVE_UNISTD_H\n" >> $$TEMPFILE &&\
 	sed -f $$TEMPFILE zconf.h.in > zconf.h.cmakein &&\
 	touch -r zconf.h.in zconf.h.cmakein &&\
 	rm $$TEMPFILE