Use a bootstrapped -O0 compiler to compile the -O2 Guile

This reduces total build time to around 30 minutes or so.

* Makefile.am (SUBDIRS): Visit bootstrap/ before module/.

* bootstrap/Makefile.am: New file.

* configure.ac: Generate bootstrap/Makefile.

* meta/uninstalled-env.in (top_builddir): Add bootstrap/ to the
  GUILE_LOAD_COMPILED_PATH.

* module/Makefile.am: Simplify to just sort files in alphabetical order;
  since bootstrap/ was already compiled, we don't need to try to
  optimize compilation order.  Although the compiler will get faster as
  more of the compiler itself is optimized, this isn't a significant
  enough effect to worry about.

Makefile.am

@@ -2,7 +2,7 @@
 ##
 ##  	Copyright (C) 1998, 1999, 2000, 2001, 2002, 2006, 2007,
 ##        2008, 2009, 2010, 2011, 2012, 2013,
-##        2014 Free Software Foundation, Inc.
+##        2014, 2015 Free Software Foundation, Inc.
 ##
 ##   This file is part of GUILE.
 ##
@@ -30,6 +30,7 @@ SUBDIRS =					\
 	lib					\
 	meta					\
 	libguile				\
+	bootstrap				\
 	module					\
 	guile-readline				\
 	examples				\