Be able to switch-off ASAN builds of our binaries.

Inroduce a way to not take a 2x performance hit when testing. It
is of importance if we run with hundreds of BTSes and 10k+ subscribers.
In the absence of using getops or shflags use an environment for it.

Change-Id: I540ba1c35e8fb72abcee0d86e0bdc1136b47345c
diff --git a/contrib/jenkins-build-osmo-mgw.sh b/contrib/jenkins-build-osmo-mgw.sh
index 5c1ce74..a04e0ca 100755
--- a/contrib/jenkins-build-osmo-mgw.sh
+++ b/contrib/jenkins-build-osmo-mgw.sh
@@ -4,9 +4,9 @@
 name="osmo-mgw"
 . "$(dirname "$0")/jenkins-build-common.sh"
 
-build_repo libosmocore --enable-sanitize --disable-doxygen
-build_repo libosmo-abis --enable-sanitize
-build_repo libosmo-netif --enable-sanitize --disable-doxygen
-build_repo osmo-mgw --enable-sanitize
+build_repo libosmocore ${SANITIZE_FLAGS} --disable-doxygen
+build_repo libosmo-abis ${SANITIZE_FLAGS}
+build_repo libosmo-netif ${SANITIZE_FLAGS} --disable-doxygen
+build_repo osmo-mgw ${SANITIZE_FLAGS}
 
 create_bin_tgz "osmo-mgw"