Bug#725143: unbuildable on some archs

[Rebecca N. Palmer]

Also, your (debian/rules) gcc version check is the wrong way round, and 
the buildds always use the first alternative build-dep (failing if it 
doesn't exist) unless you use an explicit architecture tag 
(http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=614807); fix attached.
Buildds always take the first dependency that isn't _explicitly_ marked as not for their architecture: the build will fail if the first alternative doesn't exist, even if one of the others does. (Example: https://buildd.debian.org/status/fetch.php?pkg=visp&arch=powerpc&ver=2.8.0-3&stamp=1380322503)
$ diff -up debian/control_orig debian/control
--- debian/control_orig	2013-10-17 17:37:14.876687413 +0100
+++ debian/control	2013-10-17 17:37:03.016687763 +0100
@@ -10,7 +10,7 @@ Vcs-Git: git://anonscm.debian.org/pkg-ga
 Build-Depends: debhelper (>= 9~),
                dpkg-dev (>= 1.16.1~),
                cmake (>= 2.8.0),
-               g++ (>= 4:4.8.0) | g++-4.8,
+               g++-4.8 [powerpc sparc] | g++ (>= 4:4.8.0) [mips mipsel powerpc sparc],
                pkg-config,
                libboost1.54-dev,
                libboost-atomic1.54-dev,
Make the gcc version check the right way round (ifneq (,$(findstring means if nonempty, i.e. if the string _is_ found), accept future versions, and only do it on architectures that require it.
$ diff -up debian/rules_orig debian/rules
--- debian/rules_orig	2013-10-17 17:38:26.724685290 +0100
+++ debian/rules	2013-10-17 18:15:26.360619707 +0100
@@ -22,12 +22,13 @@ endif
 
 # see #725143, some architectures fail to build because they lack
 # "__sync_fetch_and_add_8", need to link with libatomic (since ~rc2 done
-# upstrema) and depend on the version provided by GCC >= 4.8
-ifneq (,$(findstring $(shell g++ --version),"4.8"))
+# upstream) and depend on the version provided by GCC >= 4.8
+ifneq (,$(findstring $(DEB_HOST_ARCH) , mips mipsel powerpc sparc ))
+ifneq (,$(findstring $(shell dpkg --compare-versions `g++ -dumpversion` ge 4.8 || echo old),old))
 export CXX := g++-4.8
 export CC  := gcc-4.8
 endif
-
+endif
 
 DEB_HOST_MULTIARCH ?= $(shell dpkg-architecture -qDEB_HOST_MULTIARCH)