Fix recursive load for non cons hashed 'data_ephemeral_vec' content

Fix recursive load for non cons hashed 'data_ephemeral_vec' content

Removing `Vcomp_sym_subr_c_name_h' all c_name functions are GC
markable only through 'data_ephemeral_vec'.  A recursive load must not
overide its content otherwise a previously activated load will have
the original content collected before it's used.

	* src/comp.h (struct Lisp_Native_Comp_Unit): Add 'load_ongoing'
	field.

	* src/comp.c (unset_cu_load_ongoing): New function.
	(load_comp_unit): Update logic to detect and handle recursive
	loads.