misc/opennn: fix build on powerpc64
/usr/bin/c++ -DCpp11 -Dopennn_EXPORTS -fopenmp=libomp -O2 -pipe -fstack-protector-strong -fno-strict-aliasing -DNDEBUG -std=gnu++17 -fPIC -MD -MT opennn/CMakeFiles/opennn.dir/adaptive_moment_estimation.cpp.o -MF opennn/CMakeFiles/opennn.dir/adaptive_moment_estimation.cpp.o.d -o opennn/CMakeFiles/opennn.dir/adaptive_moment_estimation.cpp.o -c /wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/adaptive_moment_estimation.cpp
In file included from /wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/adaptive_moment_estimation.cpp:9:
In file included from /wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/adaptive_moment_estimation.h:32:
In file included from /wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/loss_index.h:23:
In file included from /wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/config.h:34:
In file included from /wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/../eigen/unsupported/Eigen/CXX11/Tensor:14:
In file included from /wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/../eigen/unsupported/Eigen/CXX11/../../../Eigen/Core:210:
/wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/../eigen/unsupported/Eigen/CXX11/../../../Eigen/src/Core/arch/AltiVec/PacketMath.h:1345:32: error: use of undeclared identifier 'vec_sqrt'; did you mean 'vec_rsqrt'?
BF16_TO_F32_UNARY_OP_WRAPPER(vec_sqrt, a);
^~~~~~~~
vec_rsqrt/wrkdirs/usr/ports/misc/opennn/work/opennn-6.0.4/opennn/../eigen/unsupported/Eigen/CXX11/../../../Eigen/src/Core/arch/AltiVec/PacketMath.h:1302:22: note: expanded from macro 'BF16_TO_F32_UNARY_OP_WRAPPER'
Packet4f op_even = OP(a_even);\
^/usr/lib/clang/14.0.5/include/altivec.h:8501:34: note: 'vec_rsqrt' declared here
static vector float ATTRS_o_ai vec_rsqrt(vector float a) {