Build a fasl library for ecl in addition to an executable program.

References:
* http://trac.sagemath.org/ticket/16178
* https://github.com/cschwan/sage-on-gentoo/issues/226
* https://bugs.gentoo.org/show_bug.cgi?id=499634

Index: maxima-5.29.1/src/maxima.system
===================================================================
--- maxima-5.29.1.orig/src/maxima.system
+++ maxima-5.29.1/src/maxima.system
@@ -75,6 +75,11 @@
 			     ;; Convert dir/foo.fas to dir/foo.o
 			     (make-pathname :type "o" :defaults p))
 			 files)))
+	(c::build-fasl "binary-ecl/maxima" :lisp-files obj
+			  :ld-flags
+			  (let ((x (symbol-value (find-symbol "*AUTOCONF-LD-FLAGS*"
+							      (find-package "MAXIMA")))))
+			    (if (and x (not (string= x ""))) (list x))))
 	(c::build-program "binary-ecl/maxima" :lisp-files obj
 			  :ld-flags
 			  (let ((x (symbol-value (find-symbol "*AUTOCONF-LD-FLAGS*"