patch 8.2.2104: build problem with Ruby 2.7

Problem:    Build problem with Ruby 2.7.
Solution:   Adjust function declarations. (Ozaki Kiichi, closes #7430)
diff --git a/src/configure.ac b/src/configure.ac
index 4b6794a..062c75a 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -1965,8 +1965,7 @@
 	librubyarg=`$vi_cv_path_ruby -r rbconfig -e "print $ruby_rbconfig.expand($ruby_rbconfig::CONFIG[['LIBRUBYARG']])"`
 	librubya=`$vi_cv_path_ruby -r rbconfig -e "print $ruby_rbconfig.expand($ruby_rbconfig::CONFIG[['LIBRUBY_A']])"`
 	rubylibdir=`$vi_cv_path_ruby -r rbconfig -e "print $ruby_rbconfig.expand($ruby_rbconfig::CONFIG[['libdir']])"`
-	if test -f "$rubylibdir/$librubya"; then
-	  librubyarg="$librubyarg"
+	if test -f "$rubylibdir/$librubya" || expr "$librubyarg" : "-lruby"; then
 	  RUBY_LIBS="$RUBY_LIBS -L$rubylibdir"
 	elif test "$librubyarg" = "libruby.a"; then
 	  dnl required on Mac OS 10.3 where libruby.a doesn't exist