gdb: Convert language la_lookup_symbol_nonlocal field to a method

gdb: Convert language la_lookup_symbol_nonlocal field to a method

This commit changes the language_data::la_lookup_symbol_nonlocal
function pointer member variable into a member function of
language_defn.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* ada-lang.c (ada_lookup_symbol_nonlocal): Rename to
	ada_language::lookup_symbol_nonlocal.
	(ada_language_data): Delete la_lookup_symbol_nonlocal initializer.
	(ada_language::lookup_symbol_nonlocal): New member function,
	implementation from ada_lookup_symbol_nonlocal.
	* c-lang.c (c_language_data): Delete la_lookup_symbol_nonlocal
	initializer.
	(cplus_language_data): Delete la_lookup_symbol_nonlocal
	initializer.
	(cplus_language::lookup_symbol_nonlocal): New member function.
	(asm_language_data): Delete la_lookup_symbol_nonlocal initializer.
	(minimal_language_data) Likewise.
	* cp-namespace.c (cp_lookup_nested_symbol): Update comment.
	* d-lang.c (d_language_data): Delete la_lookup_symbol_nonlocal
	initializer.
	(d_language::lookup_symbol_nonlocal): New member function.
	* f-lang.c (f_language_data): Delete la_lookup_symbol_nonlocal
	initializer.
	(f_language::lookup_symbol_nonlocal): New member function.
	* go-lang.c (go_language_data): Delete la_lookup_symbol_nonlocal
	initializer.
	* language.c (unknown_language_data): Likewise.
	(auto_language_data): Likewise.
	* language.h (language_data): Delete la_lookup_symbol_nonlocal
	field.
	(language_defn::lookup_symbol_nonlocal): New member function.
	* m2-lang.c (m2_language_data): Delete la_lookup_symbol_nonlocal
	initializer.
	* objc-lang.c (objc_language_data): Likewise.
	* opencl-lang.c (opencl_language_data): Likewise.
	* p-lang.c (pascal_language_data): Likewise.
	* rust-lang.c (rust_lookup_symbol_nonlocal): Rename to
	rust_language::lookup_symbol_nonlocal.
	(rust_language_data): Delete la_lookup_symbol_nonlocal
	initializer.
	(rust_language::lookup_symbol_nonlocal): New member function,
	implementation from rust_lookup_symbol_nonlocal.
	* symtab.c (lookup_symbol_aux): Update call to
	lookup_symbol_nonlocal.
	(basic_lookup_symbol_nonlocal): Rename to...
	(language_defn::lookup_symbol_nonlocal): ...this, and update
	header comment.  Remove language_defn parameter, and replace with
	uses of `this'.
	* symtab.h (basic_lookup_symbol_nonlocal): Delete declaration.