Fix binutils compilation error with Clang 8

[alfredo]

Summary

This change fixes the following compilation error when using clang 8 to cross compile base to powerpc64:

/usr/src/gnu/usr.bin/binutils/libopcodes/../../../../contrib/binutils/opcodes/ppc-dis.c:100:35: error: arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension [-Werror,-Wnull-pointer-arithmetic]
  info->private_data = (char *) 0 + dialect;
                       ~~~~~~~~~~ ^
1 error generated.
*** [ppc-dis.o] Error code 1

make[6]: stopped in /usr/src/gnu/usr.bin/binutils/libopcodes
1 error

Test Plan

• buildworld for x86_64 (native)
• buildworld for powerpc64 (cross)
• buildworld for powerpc64 (native)

[pfg]

LGTM.
FWIW, the GPLv3 version does an ugly calloc() dance with pointers which looks a lot more confusing.

[emaste]

LGTM to me too

[brooks]

This looks right to me.