Fix #2900 - Support more asan build flags

sys/asan.sh

@@ -1,12 +1,36 @@
 #!/bin/sh
-export CFLAGS="-fsanitize=address -lasan"
+ASAN="address leak memory undefined"
+ASAN="address"
+
+echo "========================================================================="
+echo "ASAN build script can be configured with the ASAN environment variable."
+echo "Use one of the following words to specify which build flags to use:"
+echo "  - address     - set by default, detect overflows"
+echo "  - leak        - find memory leaks"
+echo "  - memory      - detect uninitialized reads"
+echo "  - undefined   - undefined behaviour"
+echo "  - ..."
+echo "For more information:"
+echo "  http://clang.llvm.org/docs/UsersManual.html#controlling-code-generation"
+echo "For example:"
+echo "  $ ASAN='leak memory address' sys/asan.sh"
+echo "Current value:"
+echo "  ASAN=${ASAN}"
+echo "========================================================================="
+sleep 1
 export LDFLAGS="-lasan"
+
+for a in $ASAN ; do
+	export CFLAGS="${CFLAGS} -fsanitize=$a"
+done
+export CFLAGS="${CFLAGS} -lasan"
+
 echo 'int main(){return 0;}' > .a.c
 [ -z "${CC}" ] && CC=gcc
 ${CC} ${CFLAGS} ${LDFLAGS} -o .a.out .a.c
 RET=$?
 rm -f .a.out .a.c
-if [ $RET != 0 ]; then
+if [ "$RET" != 0 ]; then
 	echo "Your compiler doesn't support ASAN."
 	exit 1
 fi