gnu: boost: Patch to avoid -m32 flag on mips.

* gnu/packages/patches/boost-mips-avoid-m32.patch: New file.
* gnu-system.am (dist_patch_DATA): Register patch.
* gnu/packages/boost.scm (boost): Use it.

gnu-system.am

@@ -392,6 +392,7 @@ dist_patch_DATA =						\
   gnu/packages/patches/binutils-ld-new-dtags.patch		\
   gnu/packages/patches/binutils-loongson-workaround.patch	\
   gnu/packages/patches/bitlbee-configure-doc-fix.patch		\
+  gnu/packages/patches/boost-mips-avoid-m32.patch		\
   gnu/packages/patches/calibre-drop-unrar.patch			\
   gnu/packages/patches/calibre-no-updates-dialog.patch		\
   gnu/packages/patches/cdparanoia-fpic.patch			\

gnu/packages/boost.scm

@@ -42,7 +42,8 @@
                     ".tar.bz2"))
               (sha256
                (base32
-                "1rfkqxns60171q62cppiyzj8pmsbwp1l8jd7p6crriryqd7j1z7x"))))
+                "1rfkqxns60171q62cppiyzj8pmsbwp1l8jd7p6crriryqd7j1z7x"))
+              (patches (list (search-patch "boost-mips-avoid-m32.patch")))))
     (build-system gnu-build-system)
     (inputs `(("zlib" ,zlib)))
     (native-inputs

gnu/packages/patches/boost-mips-avoid-m32.patch

@@ -0,0 +1,15 @@
+The following patch prevents the use of the -m32 flag on mips, where it
+is not understood by gcc, as well as other non-x86 architectures.
+
+diff -u -r boost_1_58_0.orig/tools/build/src/tools/gcc.jam boost_1_58_0/tools/build/src/tools/gcc.jam
+--- boost_1_58_0.orig/tools/build/src/tools/gcc.jam	2015-04-04 19:25:07.000000000 +0200
++++ boost_1_58_0/tools/build/src/tools/gcc.jam	2015-07-10 01:08:19.822733823 +0200
+@@ -451,7 +451,7 @@
+         else
+         {
+             local arch = [ feature.get-values architecture : $(properties) ] ;
+-            if $(arch) != arm
++            if $(arch) = x86
+             {
+                 if $(model) = 32
+                 {