- make the build self-contained and cross-compile friendly: vendor the Eigen 3.4.0 headers (instead of the flaky gitlab clone / a system libeigen3-dev package), align the msvc C runtime with the dynamic one used by the rest of cross builds (xwin), and pass the -D_LIBCPP_* macros to bindgen so it parses zig's bundled libc++ regardless of ziglang/cargo-zigbuild versions

eigen/Eigen/Dense

@@ -0,0 +1,7 @@
+#include "Core"
+#include "LU"
+#include "Cholesky"
+#include "QR"
+#include "SVD"
+#include "Geometry"
+#include "Eigenvalues"