devel/glog: fix build on powerpc

In file included from /wrkdirs/usr/ports/devel/glog/work/glog-0.7.1/src/stacktrace.cc:37:
/wrkdirs/usr/ports/devel/glog/work/glog-0.7.1/src/stacktrace_powerpc-inl.h:126:4: error: Need to specify the PPC ABI for your architecture.

126 | #  error Need to specify the PPC ABI for your architecture.
    |    ^

1 error generated.