buildconf: avoid array concatenation in die()

reported as error SC2145[1] by shellcheck, but not expected to cause
any behavioural differences otherwise.

[1] https://github.com/koalaman/shellcheck/wiki/SC2145

Closes #5701

buildconf

@@ -25,7 +25,7 @@
 # die prints argument string to stdout and exits this shell script.
 #
 die(){
-  echo "buildconf: $@"
+  echo "buildconf: $*"
   exit 1
 }