ldso: defer execution of static constructors

Ldso now does not automatically execute static constructors of the
binary and shared libraries the binary depends on. If static
construction is required (e.g., if a shared library with constructor is
used or a compilation unit contains global statics) the component needs
to execute the constructors explicitly in Component::construct() via
Genode::Env::exec_static_constructors().

In the case of libc components this is done by the libc startup code
(i.e., the Component::construct() implementation in the libc).

The loading of shared objects at runtime is not affected by this change
and constructors of those objects are executed immediately.

Fixes #2332

repos/dde_ipxe/src/drivers/nic/main.cc

@@ -160,4 +160,10 @@ struct Main
 	}
 };
 
-void Component::construct(Genode::Env &env) { static Main main(env); }
+void Component::construct(Genode::Env &env)
+{
+	/* XXX execute constructors of global statics */
+	env.exec_static_constructors();
+
+	static Main main(env);
+}