Revert r340997 at the request of multiple users.

• breaks ports-mgmt/pkg build for mips64, powerpc64 and i386 for some users.

• pkg-static ---

/usr/lib/liblzma.a(stream_encoder_mt.o): In function `mythread_cond_init':
/usr/local/poudriere/jails/ppc64/usr/src/contrib/xz/src/common/mythread.h:230:
undefined reference to `pthread_condattr_init'

Reported by: jhibbits zeising