Add UMD simple assert example (#573)

examples/linux/simpleassert.c

@@ -0,0 +1,56 @@
+/**
+ * Manticore should find 5 paths, one of which should be the `return -1` error
+ * path.
+ *
+ * This code is based on the symbolic execution example in these slides:
+ * https://www.cs.umd.edu/~mwh/se-tutorial/symbolic-exec.pdf
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int main(int argc, char* argv[], char* envp[]){
+    int a;
+    int b;
+    int c;
+
+    int x = 0;
+    int y = 0;
+    int z = 0;
+
+    if (read(0, &a, sizeof(a)) != sizeof(a))
+    {
+        printf("Error reading stdin!");
+        exit(-1);
+    }
+    if (read(0, &b, sizeof(b)) != sizeof(b))
+    {
+        printf("Error reading stdin!");
+        exit(-1);
+    }
+    if (read(0, &c, sizeof(c)) != sizeof(c))
+    {
+        printf("Error reading stdin!");
+        exit(-1);
+    }
+
+    if (a) {
+        x = -2;
+    }
+
+    if (b < 5) {
+        if (!a && c) {
+            y = 1;
+        }
+        z = 2;
+    }
+
+    if (x + y + z == 3) {
+        return -1;
+    }
+
+    return 0;
+}
+
+