userland: make libs work

Working for build, but now test-user-mode-in-tree is not using --in-tree,
TODO fix later on.

lkmc/math.h

@@ -0,0 +1,20 @@
+#ifndef LKMC_MATH_H
+#define LKMC_MATH_H
+
+#include <math.h>
+#include <stdbool.h>
+
+bool lkmc_vector_equal(size_t n, double *v1, double *v2, double max_err) {
+    double sum = 0.0;
+    double diff;
+    size_t i;
+    for (i = 0; i < n; ++i) {
+        diff = v1[i] - v2[i];
+        sum += diff * diff;
+    }
+    if (sqrt(sum)/n > max_err)
+        return false;
+    return true;
+}
+
+#endif