IMPALA-10090 Pull newest code of native-toolchain before build it

If native-toolchain exists we should pull the newest code
before build it.

This change fixes the error of
I2da3ffce7abb88190be0a5ea0e2cf603f98ee15e

Change-Id: I71e23fc8a6d37d8d09565dfa38318c7dbef25c45
Reviewed-on: http://gerrit.cloudera.org:8080/16434
Reviewed-by: Quanlong Huang <huangquanlong@gmail.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
diff --git a/bin/bootstrap_system.sh b/bin/bootstrap_system.sh
index 7a51fb4..bd448e0 100755
--- a/bin/bootstrap_system.sh
+++ b/bin/bootstrap_system.sh
@@ -486,11 +486,9 @@
   if ! [[ -d "$NATIVE_TOOLCHAIN_HOME" ]]; then
     time -p git clone https://github.com/cloudera/native-toolchain/ \
       "$NATIVE_TOOLCHAIN_HOME"
-  else
-    # pull newest code of native-toolchain if exists
-    git pull
   fi
   cd "$NATIVE_TOOLCHAIN_HOME"
+  git pull
   echo "Begin build tool chain, may need several hours, please be patient...."
   sudo chmod 755 ~/.cache
   ./buildall.sh