configure.in: [Bug #8409]

* configure.in: check if prefix is same as the cwd, not only same
  path name.  also use AC_MSG_ERROR to bail out.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47152 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.in

@@ -229,9 +229,8 @@ test -z "$CXX" || ac_cv_prog_CXX="$CXX"
 if test "$program_prefix" = NONE; then
   program_prefix=
 fi
-if test "$prefix" = `pwd`; then
-  echo "--prefix cannot be the current working directory."
-  exit 1;
+if test "$prefix" -ef .; then
+  AC_MSG_ERROR(--prefix cannot be the current working directory.)
 fi
 RUBY_BASE_NAME=`echo ruby | sed "$program_transform_name"`
 RUBYW_BASE_NAME=`echo rubyw | sed "$program_transform_name"`