add libasan to the LD_PRELOAD path if it was in gnunet-config

src/util/taler-config.in

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+set -eu
+
 if ! type gnunet-config >/dev/null; then
   echo "$0 needs gnunet-config to be installed"
   exit 1
@@ -8,5 +10,8 @@ fi
 # FIXME: not very portable ...
 # FIXME: should use "libdir" instead of prefix/lib, but somehow
 # the recursive expansion does not work ;-(.
-export LD_PRELOAD=@prefix@/lib/libtalerutil.so
+GC=`which gnunet-config`
+ASAN=""
+A=`ldd $GC | grep libasan` && ASAN=`echo $A | awk '{print $3 ":"}'`
+export LD_PRELOAD=${ASAN}${LD_PRELOAD:-}:@prefix@/lib/libtalerutil.so
 exec gnunet-config "$@"