Demos: Add a dynamic linking demo to show off dlfcn methods

The LinkDemo program calls dlopen/dlsym/dlclose to try and load
a dyanmic library from /usr/lib. It read a global variable and
calls a global function (extern "C" of course :) ).

There a few hacks left in the LinkLib dynamic library, however.
In order to get the linker to stop complaining, we have to use
-nostartfiles -ffreestanding otherwise it will link crt0.o to our
shared object, which is definitely not right as the _init function
for a main program (that calls main) is not suitable for our lib

Demos/DynamicLink/LinkDemo/main.cpp

@@ -0,0 +1,72 @@
+#include <AK/String.h>
+
+#include <dlfcn.h>
+#include <stdio.h>
+
+int main()
+{
+    void* handle = dlopen("/usr/lib/libDynamicLib.so", RTLD_LAZY | RTLD_GLOBAL);
+
+    if (!handle) {
+        printf("Failed to dlopen! %s\n", dlerror());
+        return 1;
+    }
+
+    // Test getting an external variable from the library and read it out
+    int* ptr_global = (int*)dlsym(handle, "global_lib_variable");
+
+    if (!ptr_global) {
+        printf("Failed to dlsym for \"global_lib_variable\"! %s\n", dlerror());
+        return 2;
+    }
+
+    printf("Found global lib variable address: %p\n", ptr_global);
+
+    printf("Global lib variable is %d\n", *ptr_global);
+
+    // Test getting a method from the library and calling it
+    void (*lib_func)(void) = (void (*)(void))dlsym(handle, "global_lib_function");
+
+    printf("Found global lib function address: %p\n", lib_func);
+
+    if (!lib_func) {
+        printf("Failed to dlsym for \"global_lib_function\"! %s\n", dlerror());
+        return 2;
+    }
+
+    lib_func();
+
+    printf("I think I called my lib function!\n");
+
+    // Test getting a method that takes and returns arugments now
+    const char* (*other_func)(int) = (const char* (*)(int))dlsym(handle, "other_lib_function");
+
+    printf("Found other lib function address %p\n", other_func);
+
+    if (!other_func) {
+        printf("Failed to dlsym for \"other_lib_function\"! %s\n", dlerror());
+        return 2;
+    }
+
+    // Call it twice with different arguments
+    String formatted_result = other_func(10);
+
+    printf("(%d + %d = %d) %s\n", *ptr_global, 10, *ptr_global + 10, formatted_result.characters());
+
+    *ptr_global = 17;
+
+    formatted_result = other_func(5);
+
+    printf("(%d + %d = %d) %s\n", *ptr_global, 5, *ptr_global + 5, formatted_result.characters());
+
+    int ret = dlclose(handle);
+
+    if (ret < 0) {
+        printf("Failed to dlclose! %s\n", dlerror());
+        return 3;
+    }
+
+    printf("Bye for now!\n");
+
+    return 0;
+}