When unit testing is enabled, make sure _ASSERT() is not already
defined by the host environment before defining _ASSERT(). This
avoids conflicts with VS20xx builds of GoogleTest based unit tests.
Cc: Liming Gao <gaoliming@byosoft.com.cn> Cc: Zhiguang Liu <zhiguang.liu@intel.com> Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com> Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>