gnu: gcc: Work around ARM bootstrapping failure (GCC bug #71399).

* gnu/packages/patches/gcc-arm-bug-71399.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/gcc.scm (gcc-4.9)[source]: Use it.

gnu/local.mk

@@ -515,6 +515,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/fontforge-svg-modtime.patch		\
   %D%/packages/patches/freeimage-CVE-2015-0852.patch		\
   %D%/packages/patches/gawk-shell.patch				\
+  %D%/packages/patches/gcc-arm-bug-71399.patch			\
   %D%/packages/patches/gcc-arm-link-spec-fix.patch		\
   %D%/packages/patches/gcc-cross-environment-variables.patch	\
   %D%/packages/patches/gcc-libvtv-runpath.patch			\

gnu/packages/gcc.scm

@@ -340,7 +340,8 @@ Go.  It also includes runtime support libraries for these languages.")
               (sha256
                (base32
                 "14l06m7nvcvb0igkbip58x59w3nq6315k6jcz3wr9ch1rn9d44bc"))
-              (patches (search-patches "gcc-libvtv-runpath.patch"))))))
+              (patches (search-patches "gcc-arm-bug-71399.patch"
+                                       "gcc-libvtv-runpath.patch"))))))
 
 (define-public gcc-5
   ;; Note: GCC >= 5 ships with .info files but 'make install' fails to install

gnu/packages/patches/gcc-arm-bug-71399.patch

@@ -0,0 +1,55 @@
+Revert the following commit to work around a bootstrap comparison failure on
+ARMv7, as reported at <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71399>.
+
+commit f6ab85b7049a03962ea98924d00802da357a1ad3
+Author: renlin <renlin@138bc75d-0d04-0410-961f-82ee72b054a4>
+Date:   Wed Dec 2 14:06:31 2015 +0000
+
+    [PR67383][ARM][4.9]Backport of "Allow any register for DImode values in Thumb2"
+    
+    This partially fix PR67383. It allows the reload more flexibility to choose
+    spilling pseudo registers.
+    
+    
+    gcc/ChangeLog:
+    
+    2015-12-02  Renlin Li  <renlin.li@arm.com>
+    
+            Backport from mainline.
+            2014-04-22  Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>
+    
+            * config/arm/arm.c (arm_hard_regno_mode_ok): Loosen
+            restrictions on core registers for DImode values in Thumb2.
+    
+    
+    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-4_9-branch@231177 138bc75d-0d04-0410-961f-82ee72b054a4
+
+diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
+index 8ba6060..d9028a1 100644
+--- b/gcc/config/arm/arm.c
++++ a/gcc/config/arm/arm.c
+@@ -22624,19 +22624,12 @@
+     }
+ 
+   /* We allow almost any value to be stored in the general registers.
+-     Restrict doubleword quantities to even register pairs in ARM state
+-     so that we can use ldrd.  Do not allow very large Neon structure
+-     opaque modes in general registers; they would use too many.  */
++     Restrict doubleword quantities to even register pairs so that we can
++     use ldrd.  Do not allow very large Neon structure opaque modes in
++     general registers; they would use too many.  */
+   if (regno <= LAST_ARM_REGNUM)
+-    {
+-      if (ARM_NUM_REGS (mode) > 4)
+-	  return FALSE;
+-
+-      if (TARGET_THUMB2)
+-	return TRUE;
+-
+-      return !(TARGET_LDRD && GET_MODE_SIZE (mode) > 4 && (regno & 1) != 0);
+-    }
++    return !(TARGET_LDRD && GET_MODE_SIZE (mode) > 4 && (regno & 1) != 0)
++      && ARM_NUM_REGS (mode) <= 4;
+ 
+   if (regno == FRAME_POINTER_REGNUM
+       || regno == ARG_POINTER_REGNUM)