[ELF] Remove dependency on hexdump from lit tests

[jhenderson]

Summary

hexdump is not part of the GNU coreutils, and so is not required to be able to build and test LLVM, according to the documentation. This change removes the dependency on hexdump from a lit test.

[grimar]

LGTM, thanks !

[davide]

LGTM, thanks James.

lld/trunk/test/ELF/fill-trap.s

 # REQUIRES: x86
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: ld.lld %t -o %t2
 # RUN: llvm-readobj -program-headers %t2 | FileCheck %s
-# RUN: hexdump -v -s 0x0001ff0 -x %t2 | FileCheck %s -check-prefix=FILL
+# RUN: od -Ax -x -N16 -j0x1ff0 %t2 | FileCheck %s -check-prefix=FILL
 
 # CHECK: ProgramHeader {
 # CHECK:   Type: PT_LOAD
 # CHECK:   Offset: 0x1000
 # CHECK-NEXT:   VirtualAddress:
 # CHECK-NEXT:   PhysicalAddress:
 # CHECK-NEXT:   FileSize: 4096
 # CHECK-NEXT:   MemSize:
 # CHECK-NEXT:   Flags [
 # CHECK-NEXT:     PF_R
 # CHECK-NEXT:     PF_X
 # CHECK-NEXT:   ]
 
-## Check that executable page is filled with traps at it's end.
-# FILL: 0001ff0 cccc cccc cccc cccc cccc cccc cccc cccc
+## Check that executable page is filled with traps at its end.
+# FILL: 001ff0 cccc cccc cccc cccc cccc cccc cccc cccc
 
 .globl _start
 _start:
   nop