gnu: ola: Build with protobuf@2.

This follows up commit dd12d4aad0.

* gnu/packages/protobuf.scm (protobuf-2): New variable.
* gnu/packages/lighting.scm (ola)[propagated-inputs]: Use it.

gnu/packages/lighting.scm

@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2016 John J. Foerch <jjfoerch@earthlink.net>
+;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -59,7 +60,9 @@
        ("libuuid" ,util-linux)
        ("zlib" ,zlib)))
     (propagated-inputs
-     `(("protobuf" ,protobuf))) ;; for pkg-config --libs libola
+     ;; Ola 0.10.5 only supports protobuf 2.x, and building it with 3.x breaks.
+     ;; XXX Remove protobuf-2 when it is no longer needed.
+     `(("protobuf" ,protobuf-2))) ;; for pkg-config --libs libola
     (arguments
      `(;; G++ >= 4.8 macro expansion tracking requires lots of memory, causing
        ;; build to fail on low memory systems.  We disable that with the

gnu/packages/protobuf.scm

@@ -3,6 +3,7 @@
 ;;; Copyright © 2016 Daniel Pimentel <d4n1@d4n1.org>
 ;;; Copyright © 2016 Leo Famulari <leo@famulari.name>
 ;;; Copyright © 2017 Ricardo Wurmus <rekado@elephly.net>
+;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -53,6 +54,19 @@ yet extensible format.  Google uses Protocol Buffers for almost all of its
 internal RPC protocols and file formats.")
     (license bsd-3)))
 
+;; XXX Remove this old version when no other packages depend on it.
+(define-public protobuf-2
+  (package (inherit protobuf)
+    (version "2.6.1")
+    (source (origin
+              (method url-fetch)
+              (uri (string-append "https://github.com/google/protobuf/releases/"
+                                  "download/v" version "/protobuf-"
+                                  version ".tar.bz2"))
+              (sha256
+               (base32
+                "040rcs9fpv4bslhiy43v7dcrzakz4vwwpyqg4jp8bn24sl95ci7f"))))))
+
 (define-public protobuf-c
   (package
     (name "protobuf-c")