python: add missing host build dependency on expat/host

Since 94f87dc1, host build of Python depends on expat installed in host
staging directory. However, pyexpat extension fails to build if expat
was not built and installed to staging dir before - adding host build
dependency should fix this.

Signed-off-by: Jan Čermák <jan.cermak@nic.cz>

lang/python/Makefile

@@ -29,7 +29,7 @@ PKG_BUILD_DIR:=$(BUILD_DIR)/Python-$(PKG_VERSION)
 HOST_BUILD_DIR:=$(BUILD_DIR_HOST)/Python-$(PKG_VERSION)
 
 PKG_BUILD_DEPENDS:=python/host
-HOST_BUILD_DEPENDS:=bzip2/host
+HOST_BUILD_DEPENDS:=bzip2/host expat/host
 
 include $(INCLUDE_DIR)/host-build.mk
 include $(INCLUDE_DIR)/package.mk