build: Add --enable-neuron to distcheck flags

Distcheck was broken for Neuron builds, not because of any functional
issue but the build flag to enable neuron was not passed through to
automake.

Signed-off-by: Raghu Raja <raghunch@amazon.com>

m4/check_pkg_neuron.m4

@@ -11,6 +11,7 @@ AC_DEFUN([CHECK_PKG_NEURON], [
 
   AS_IF([test "${enable_neuron}" = "yes"],
         [check_pkg_define=1
+         NCCL_NET_OFI_DISTCHCK_CONFIGURE_FLAGS="$NCCL_NET_OFI_DISTCHCK_CONFIGURE_FLAGS --enable-neuron"
          $1],
         [check_pkg_define=0
          $2])