LibC: Run constructors on process startup.

Cooperate with the compiler to generate and execute the _init_array list
of constructor functions on userspace program statup. This took two days
to get working, my goodness. :^)

AK/StdLibExtras.cpp

@@ -52,6 +52,8 @@ void* mmx_memcpy(void* dest, const void* src, size_t len)
     return dest;
 }
 
+#ifdef KERNEL
+
 static inline uint32_t divq(uint64_t n, uint32_t d)
 {
     uint32_t n1 = n >> 32;
@@ -144,5 +146,6 @@ uint64_t __udivmoddi4(uint64_t n, uint64_t d, uint64_t* r)
 
     return q;
 }
+#endif
 
 }