--- nfs-utils-2.4.3/configure.ac.orig	2020-02-09 20:41:19.000000000 +0100
+++ nfs-utils-2.4.3/configure.ac	2020-05-16 10:00:17.813179249 +0200
@@ -622,7 +622,7 @@
   AC_MSG_CHECKING([whether CC supports $1])
   AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
     [AC_MSG_RESULT([yes])]
-    [$2+=$1],
+    [$2="$$2 $1"],
     [AC_MSG_RESULT([no])]
   )
   CFLAGS="$my_save_cflags"