build-setup: enable the shared state cache

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/build-setup.sh b/build-setup.sh
index ca51041..4b1b919 100755
--- a/build-setup.sh
+++ b/build-setup.sh
@@ -178,6 +178,7 @@
 INHERIT += "rm_work"
 BB_GENERATE_MIRROR_TARBALLS = "1"
 DL_DIR="${HOME}/bitbake_downloads"
+SSTATE_DIR="${HOME}/bitbake_sharedstatecache"
 USER_CLASSES += "buildstats"
 EOF_CONF