jenkins: add 'make V=1' for more verbose build logs

In the logs, it is nice to see whether e.g. sanitize or -Werror args actually
made it to the gcc command line. With V=1 we see the complete command
invocations that would be hidden otherwise.

Change-Id: Ie89b1c39489ba80fb47716f4c747f2c85960e32e
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index 5798c95..c341d05 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -16,7 +16,7 @@
     prep_build "$src_dir" "$build_dir"
 
     "$src_dir"/configure --enable-static $ENABLE_SANITIZE CFLAGS="-Werror" CPPFLAGS="-Werror"
-    $MAKE $PARALLEL_MAKE check \
+    $MAKE V=1 $PARALLEL_MAKE check \
         || cat-testlogs.sh
 }