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💯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)
Submitted by: alfredo.junior_eldorado.org.br
Reviewed By: emaste, pfg, brooks
Differential Revision: https://reviews.freebsd.org/D19235
9b0c6f1624