Mark big and mach with ATTRIBUTE_UNUSED

Fix build on x86:

opcodes/disassemble.c: In function ‘disassembler’:
opcodes/disassemble.c:113:52: error: unused parameter ‘big’ [-Werror=unused-parameter]
 disassembler (enum bfd_architecture a, bfd_boolean big, unsigned long mach,
                                                    ^~~
opcodes/disassemble.c:113:71: error: unused parameter ‘mach’ [-Werror=unused-parameter]
 disassembler (enum bfd_architecture a, bfd_boolean big, unsigned long mach,
                                                                       ^~~~
cc1: all warnings being treated as errors

	* disassemble.c (disassembler): Mark big and mach with
	ATTRIBUTE_UNUSED.

opcodes/ChangeLog

@@ -1,3 +1,8 @@
+2017-08-07  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* disassemble.c (disassembler): Mark big and mach with
+	ATTRIBUTE_UNUSED.
+
 2017-08-07  Maciej W. Rozycki  <macro@imgtec.com>
 
 	* disassemble.c (disassembler): Remove arch/mach/endian

opcodes/disassemble.c

@@ -110,7 +110,9 @@
 #endif
 
 disassembler_ftype
-disassembler (enum bfd_architecture a, bfd_boolean big, unsigned long mach,
+disassembler (enum bfd_architecture a,
+	      bfd_boolean big ATTRIBUTE_UNUSED,
+	      unsigned long mach ATTRIBUTE_UNUSED,
 	      bfd *abfd ATTRIBUTE_UNUSED)
 {
   disassembler_ftype disassemble;