Fix qt4 ports on armv6.

Due to a misspelling in GCC [1] (probably) the check for the ARMv6KZ platform
used ARM_ARCH_6ZK instead of ARM_ARCH_6KZ.

[1] https://gcc.gnu.org/ml/gcc-patches/2015-06/msg01679.html

PR: 210027
Submitted by: Mikaël Urankar <mikael.urankar@gmail.com>
Reviewed by: rakuco
Differential Revision: https://reviews.freebsd.org/D8322