lua-wsapi: build each variant in its own dir

This avoids unnecessary package rebuilds, when running make back to
back.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>

lang/lua-wsapi/Makefile

@@ -9,12 +9,12 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=lua-wsapi
 PKG_VERSION:=1.7
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://codeload.github.com/keplerproject/wsapi/tar.gz/v$(PKG_VERSION)?
 PKG_HASH:=48dc7aba0fd2e96a3e5ef51045b5d923964f6ae299de761aa0467031ad44e987
-PKG_BUILD_DIR:=$(BUILD_DIR)/wsapi-$(PKG_VERSION)
+PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(BUILD_VARIANT)/wsapi-$(PKG_VERSION)
 
 PKG_MAINTAINER:=Dirk Chang <dirk@kooiot.com>
 PKG_LICENSE:=MIT