gdb: Convert language la_pass_by_reference field to a method

gdb: Convert language la_pass_by_reference field to a method

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

The interesting thing in this commit is that I have removed the
default_pass_by_reference function entirely.  This function only ever
returned a language_pass_by_ref_info struct in its default state, so
all uses of this function can be replaced by just default
initialisation of a language_pass_by_ref_info variable.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* ada-lang.c (ada_language_data): Delete la_pass_by_reference
	initializer.
	* c-lang.c (c_language_data): Likewise.
	(cplus_language_data): Likewise.
	(cplus_language::pass_by_reference_info): New method.
	(asm_language_data): Delete la_pass_by_reference initializer.
	(minimal_language_data): Likewise.
	* cp-abi.c (cp_pass_by_reference): Remove use of
	default_pass_by_reference.
	* d-lang.c (d_language_data): Likewise.
	* f-lang.c (f_language_data): Likewise.
	* gnu-v3-abi.c (gnuv3_pass_by_reference): Remove use of
	default_pass_by_reference.
	* go-lang.c (go_language_data): Likewise.
	* language.c (language_pass_by_reference): Update.
	(default_pass_by_reference): Delete.
	(unknown_language_data): Delete la_pass_by_reference
	initializer.
	(auto_language_data): Likewise.
	* language.h (struct language_data): Delete la_pass_by_reference
	field.
	(language_defn::pass_by_reference_info): New member function.
	(default_pass_by_reference): Delete declaration.
	* m2-lang.c (m2_language_data): Delete la_pass_by_reference
	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_language_data): Likewise.