patch 8.1.0612: cannot use two global runtime dirs with configure

Problem:    Cannot use two global runtime dirs with configure.
Solution:   Support a comma in --with-global-runtime. (James McCoy,
            closes #3704)
diff --git a/src/auto/configure b/src/auto/configure
index 825d5da..3a1495b 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -1533,7 +1533,7 @@
   --with-vim-name=NAME    what to call the Vim executable
   --with-ex-name=NAME     what to call the Ex executable
   --with-view-name=NAME   what to call the View executable
-  --with-global-runtime=DIR    global runtime directory in 'runtimepath'
+  --with-global-runtime=DIR    global runtime directory in 'runtimepath', comma-separated for multiple directories
   --with-modified-by=NAME       name of who modified a release version
   --with-features=TYPE    tiny, small, normal, big or huge (default: huge)
   --with-compiledby=NAME  name to show in :version message
@@ -4890,17 +4890,26 @@
 
 # Check whether --with-global-runtime was given.
 if test "${with_global_runtime+set}" = set; then :
-  withval=$with_global_runtime; { $as_echo "$as_me:${as_lineno-$LINENO}: result: $withval" >&5
-$as_echo "$withval" >&6; }; cat >>confdefs.h <<_ACEOF
-#define RUNTIME_GLOBAL "$withval"
-_ACEOF
-
+  withval=$with_global_runtime; RUNTIME_GLOBAL="$withval"; { $as_echo "$as_me:${as_lineno-$LINENO}: result: $withval" >&5
+$as_echo "$withval" >&6; }
 else
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
 $as_echo "no" >&6; }
 fi
 
 
+if test "X$RUNTIME_GLOBAL" != "X"; then
+  RUNTIME_GLOBAL_AFTER=$(printf -- "$RUNTIME_GLOBAL\\n" | $AWK -F, 'BEGIN { comma=0 } { for (i = NF; i > 0; i--) { if (comma) { printf ",%s/after", $i } else { printf "%s/after", $i; comma=1 } } } END { printf "\n" }')
+  cat >>confdefs.h <<_ACEOF
+#define RUNTIME_GLOBAL "$RUNTIME_GLOBAL"
+_ACEOF
+
+  cat >>confdefs.h <<_ACEOF
+#define RUNTIME_GLOBAL_AFTER "$RUNTIME_GLOBAL_AFTER"
+_ACEOF
+
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking --with-modified-by argument" >&5
 $as_echo_n "checking --with-modified-by argument... " >&6; }