/usr/src/gcc-5/debian/patches/cross-fixes.diff is in gcc-5-source 5.5.0-12ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 | # DP: Fix the linker error when creating an xcc for ia64
---
 gcc/config/ia64/fde-glibc.c     |    3 +++
 gcc/config/ia64/unwind-ia64.c   |    3 ++-
 gcc/unwind-compat.c             |    2 ++
 gcc/unwind-generic.h            |    2 ++
 6 files changed, 14 insertions(+), 1 deletions(-)
Index: b/src/libgcc/config/ia64/fde-glibc.c
===================================================================
--- a/src/libgcc/config/ia64/fde-glibc.c
+++ b/src/libgcc/config/ia64/fde-glibc.c
@@ -28,6 +28,7 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE 1
 #endif
+#ifndef inhibit_libc
 #include "config.h"
 #include <stddef.h>
 #include <stdlib.h>
@@ -159,3 +160,5 @@
 
   return data.ret;
 }
+
+#endif
Index: b/src/libgcc/config/ia64/unwind-ia64.c
===================================================================
--- a/src/libgcc/config/ia64/unwind-ia64.c
+++ b/src/libgcc/config/ia64/unwind-ia64.c
@@ -27,6 +27,7 @@
    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    <http://www.gnu.org/licenses/>.  */
 
+#ifndef inhibit_libc
 #include "tconfig.h"
 #include "tsystem.h"
 #include "coretypes.h"
@@ -2467,3 +2468,4 @@
 #endif
 
 #endif
+#endif
Index: b/src/libgcc/unwind-compat.c
===================================================================
--- a/src/libgcc/unwind-compat.c
+++ b/src/libgcc/unwind-compat.c
@@ -24,6 +24,7 @@
    <http://www.gnu.org/licenses/>.  */
 
 #if defined (USE_GAS_SYMVER) && defined (USE_LIBUNWIND_EXCEPTIONS)
+#ifndef inhibit_libc
 #include "tconfig.h"
 #include "tsystem.h"
 #include "unwind.h"
@@ -208,3 +209,4 @@
 }
 symver (_Unwind_SetIP, GCC_3.0);
 #endif
+#endif
Index: b/src/libgcc/unwind-generic.h
===================================================================
--- a/src/libgcc/unwind-generic.h
+++ b/src/libgcc/unwind-generic.h
@@ -221,6 +221,7 @@
    compatible with the standard ABI for IA-64, we inline these.  */
 
 #ifdef __ia64__
+#ifndef inhibit_libc
 #include <stdlib.h>
 
 static inline _Unwind_Ptr
@@ -239,6 +240,7 @@
 
 /* @@@ Retrieve the Backing Store Pointer of the given context.  */
 extern _Unwind_Word _Unwind_GetBSP (struct _Unwind_Context *);
+#endif
 #else
 extern _Unwind_Ptr _Unwind_GetDataRelBase (struct _Unwind_Context *);
 extern _Unwind_Ptr _Unwind_GetTextRelBase (struct _Unwind_Context *);
 |