zlib: Fix build

Using "make -j $(N)" with N > 1 sometimes breaks zlib build.

Signed-off-by: Lionel Landwerlin <llandwerlin@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

CHANGES

@@ -24,7 +24,7 @@
 	pango, pcre, php, prboom, radvd, qt, samba, sdl_sound,
 	shared-mime-info, speex, sqlite, strace, taglib, tcpdump,
 	tiff, tn5250, udev, udpcast, usbmount, usbutils, which,
-	xlib_libX11
+	xlib_libX11, zlib
 
 	Removed packages: dillo, libglib12, libgtk12, microwin,
 	pcmcia

package/zlib/zlib.mk

@@ -42,11 +42,11 @@ define HOST_ZLIB_CONFIGURE_CMDS
 endef
 
 define ZLIB_BUILD_CMDS
-	$(MAKE) -C $(@D) all libz.a
+	$(MAKE1) -C $(@D) all libz.a
 endef
 
 define HOST_ZLIB_BUILD_CMDS
-	$(MAKE) -C $(@D) all libz.a
+	$(MAKE1) -C $(@D) all libz.a
 endef
 
 define ZLIB_INSTALL_STAGING_CMDS