LibC: Add some things needed to build GNU bc.

This patch adds vprintf(), sig_atomic_t, random() and strdup().
bc doesn't build yet, but it will.

LibC/stdlib.cpp

@@ -252,4 +252,14 @@ int abs(int i)
     return i < 0 ? -i : i;
 }
 
+long int random()
+{
+    return rand();
+}
+
+void srandom(unsigned seed)
+{
+    srand(seed);
+}
+
 }