commit 7dd1ea4cabade8c95cda5e677951e3b08f793487
Author: Andrew Johnson <anj@anl.gov>
Date:   Mon Sep 17 10:24:51 2018 -0500

    GNU Make 3.81 (as used on Travis) doesn't have 'undefine'

diff --git configure/CONFIG configure/CONFIG
index f5ba0b7..b51a9d3 100644
--- configure/CONFIG
+++ configure/CONFIG
@@ -27,7 +27,7 @@ ifeq ($(origin EPICS_HOST_ARCH), undefined)
         $(TOP)/src/tools/EpicsHostArch.pl))
   # NB: We use a simply expanded variable here for performance:
   export EPICS_HOST_ARCH := $(shell perl $(EHA))
-  undefine EHA
+  EHA :=
 endif
 
 -include $(CONFIG)/os/CONFIG_COMPAT