gnu: binutils: Work around Bash 4.2 bug.

Fixes a 'binutils-cross-boot0' build failure on mips64el.

Reported at
<https://lists.gnu.org/archive/html/guix-devel/2016-09/msg01083.html>.

* gnu/packages/patches/binutils-mips-bash-bug.patch: New file.
* gnu/packages/base.scm (binutils)[source]: Use it.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/local.mk

@@ -455,6 +455,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/bigloo-gc-shebangs.patch			\
   %D%/packages/patches/binutils-ld-new-dtags.patch		\
   %D%/packages/patches/binutils-loongson-workaround.patch	\
+  %D%/packages/patches/binutils-mips-bash-bug.patch		\
   %D%/packages/patches/byobu-writable-status.patch		\
   %D%/packages/patches/calibre-drop-unrar.patch			\
   %D%/packages/patches/calibre-no-updates-dialog.patch		\

gnu/packages/base.scm

@@ -386,7 +386,8 @@ change.  GNU make offers many powerful extensions over the standard utility.")
              (base32
               "125clslv17xh1sab74343fg6v31msavpmaa1c1394zsqa773g5rn"))
             (patches (search-patches "binutils-ld-new-dtags.patch"
-                                     "binutils-loongson-workaround.patch"))))
+                                     "binutils-loongson-workaround.patch"
+                                     "binutils-mips-bash-bug.patch"))))
    (build-system gnu-build-system)
 
    ;; TODO: Add dependency on zlib + those for Gold.

gnu/packages/patches/binutils-mips-bash-bug.patch

@@ -0,0 +1,22 @@
+Bash 4.2.0(1)-release, which we use during bootstrap, does not yield the
+"x" case in:
+
+  case x"$EMULATION_NAME" in x) ;; *) ;; esac
+
+when 'EMULATION_NAME' is undefined.  Bash 4.3.30(1)-release doesn't have this
+problem.  Work around it.
+
+This Bash bug was fixed
+in <http://ftp.gnu.org/gnu/bash/bash-4.2-patches/bash42-007>.
+
+--- a/ld/emulparams/elf32bmipn32-defs.sh
++++ b/ld/emulparams/elf32bmipn32-defs.sh
+@@ -13,7 +13,7 @@ LITTLE_OUTPUT_FORMAT="elf32-littlemips"
+ TEMPLATE_NAME=elf32
+ EXTRA_EM_FILE=mipself
+ 
+-case x"$EMULATION_NAME" in
++case "x$EMULATION_NAME" in
+ xelf32*n32*) ELFSIZE=32 ;;
+ xelf64*) ELFSIZE=64 ;;
+ x) ;;