flex-native: create a wrapper script for sstate installation

flex-native encodes M4 staging path in its binary, which breaks sstate
installation in a new build environment. Use create_wrapper to create
a wrapper script which explicitly set M4 environmental variable to the
new path

Signed-off-by: Kevin Tian <kevin.tian@intel.com>

meta/recipes-devtools/flex/flex.inc

@@ -11,3 +11,6 @@ SRC_URI = "${SOURCEFORGE_MIRROR}/flex/flex-${PV}.tar.bz2 "
 
 inherit autotools
 
+do_install_append_virtclass-native() {
+	create_wrapper ${D}/${bindir}/flex M4=${STAGING_BINDIR_NATIVE}/m4
+}

meta/recipes-devtools/flex/flex_2.5.35.bb

@@ -1,5 +1,5 @@
 require flex.inc
-PR = "r1"
+PR = "r2"
 LICENSE="BSD"
 LIC_FILES_CHKSUM = "file://COPYING;md5=e4742cf92e89040b39486a6219b68067"
 BBCLASSEXTEND = "native"