postgresql: add HOST_BUILD_DEPENDS:=zlib/host

spotted on buildbot trying postgresql/host build:
configure: error: zlib library not found

Fix this by adding zlib/host to HOST_BUILD_DEPENDS.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

libs/postgresql/Makefile

@@ -21,7 +21,8 @@ PKG_HASH:=2e8c8446ba94767bda8a26cf5a2152bf0ae68a86aaebf894132a763084579d84
 PKG_USE_MIPS16:=0
 PKG_FIXUP:=autoreconf
 PKG_MACRO_PATHS:=config
-PKG_BUILD_DEPENDS += readline/host postgresql/host
+PKG_BUILD_DEPENDS:=readline/host postgresql/host
+HOST_BUILD_DEPENDS:=zlib/host
 PKG_INSTALL:=1
 
 include $(INCLUDE_DIR)/host-build.mk