check for __ARM_NEON instead as it's defined in arm64 as well
add EIGEN_TEST_NEON64, but it's a dummy, AArch64 implies NEON support so extra CXXFLAGS are needed
working 64-bit support in PacketMath.h, Complex.h needed
Added ARMv8 support
Merged eigen/eigen into default
Merged in kmargar/eigen (pull request #87)

Extend NEON to add ARMv8 64-bit double support
Temporary workaround for bug 875:
Let TriangularView<Sparse>::nonZeros() return nonZeros() of the nested expression
Bug 898: add inline hint to const_cast_ptr