luaposix: Fix LUA_INCDIR path

If not specified on build commandline for luke, it results in
pulling it from build host development headers under /usr/include
this was always happening but with recent fixes to GCC poisoning
host includes patch, this issue has come to fore.

Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-devtools/luaposix/luaposix_36.2.1.bb

@@ -16,7 +16,7 @@ B = "${S}"
 inherit pkgconfig
 
 do_compile() {
-    ${S}/build-aux/luke
+    ${S}/build-aux/luke LUA_INCDIR=${STAGING_INCDIR}
 }
 
 do_install() {