configure.in: with-destdir

* configure.in: add --with-destdir option which sets default
  destination directory to install.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46857 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Makefile.in

@@ -184,6 +184,8 @@ MESSAGE_END = ; do echo "$$line"; done
 ECHO_BEGIN = @sep=''; for word in
 ECHO_END = ; do echo @ECHO_N@ "$$sep'$$word'@ECHO_C@"; sep=' '; done; echo
 
+DESTDIR       = @DESTDIR@
+
 configure_args = @configure_args@
 #### End of variables
 

configure.in

@@ -4185,6 +4185,11 @@ AC_ARG_WITH([ruby-pc],
 AC_SUBST(ruby_pc)
 AC_SUBST(exec, [exec])
 
+AC_ARG_WITH(destdir,
+	    AS_HELP_STRING([--with-destdir=DESTDIR], [specify default directory to install]),
+	    [DESTDIR="$withval"])
+AC_SUBST(DESTDIR)
+
 AC_CONFIG_FILES($ruby_pc:template/ruby.pc.in,
     [
     if sed ['s/\$(\([A-Za-z_][A-Za-z0-9_]*\))/${\1}/g;s/@[A-Za-z_][A-Za-z0-9_]*@//'] $ruby_pc > ruby.tmp.pc &&