Fix link flags for Ruby

Fix #468

configure script had an issue that linker always links system Ruby framework.

    $ configure --enable-rubyinterp=yes --with-ruby-command=/usr/bin/ruby
    $ grep RUBY_LIBS src/auto/config.mk
    RUBY_LIBS= -framework Ruby

    $ configure --enable-rubyinterp=yes --with-ruby-command=/usr/local/bin/ruby
    $ grep RUBY_LIBS src/auto/config.mk
    RUBY_LIBS= -framework Ruby

After this commit, configure will pick right library settings from Ruby

    $ configure --enable-rubyinterp=yes --with-ruby-command=/usr/bin/ruby
    $ grep RUBY_LIBS src/auto/config.mk
    RUBY_LIBS= -framework Ruby

    $ configure --enable-rubyinterp=yes --with-ruby-command=/usr/local/bin/ruby
    $ grep RUBY_LIBS src/auto/config.mk
    RUBY_LIBS= -lruby.2.4.0 -lpthread -ldl -lobjc

Author: splhack

src/auto/configure

@@ -7262,7 +7262,7 @@ $as_echo "$rubyhdrdir" >&6; }
 	if test -f "$rubylibdir/$librubya"; then
 	  librubyarg="$librubyarg"
 	  RUBY_LIBS="$RUBY_LIBS -L$rubylibdir"
-        elif test -d "/System/Library/Frameworks/Ruby.framework"; then
+        elif test "$vi_cv_path_ruby" = "/usr/bin/ruby" -a -d "/System/Library/Frameworks/Ruby.framework"; then
                         RUBY_LIBS="-framework Ruby"
                         RUBY_CFLAGS="$RUBY_CFLAGS -DRUBY_VERSION=$rubyversion"
             librubyarg=

src/configure.ac

@@ -1930,7 +1930,7 @@ if test "$enable_rubyinterp" = "yes" -o "$enable_rubyinterp" = "dynamic"; then
 	if test -f "$rubylibdir/$librubya"; then
 	  librubyarg="$librubyarg"
 	  RUBY_LIBS="$RUBY_LIBS -L$rubylibdir"
-        elif test -d "/System/Library/Frameworks/Ruby.framework"; then
+        elif test "$vi_cv_path_ruby" = "/usr/bin/ruby" -a -d "/System/Library/Frameworks/Ruby.framework"; then
             dnl On Mac OS X it is safer to just use the -framework flag
             RUBY_LIBS="-framework Ruby"
             dnl Don't include the -I flag when -framework is set