gdb: Convert language skip_trampoline field to a method

gdb: Convert language skip_trampoline field to a method

This commit changes the language_data::skip_trampoline 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_language_data): Delete skip_trampoline
	initializer.
	* c-lang.c (c_language_data): Likewise.
	(cplus_language_data): Likewise.
	(cplus_language::skip_trampoline): New member function.
	(asm_language_data): Delete skip_trampoline initializer.
	(minimal_language_data): Likewise.
	* d-lang.c (d_language_data): Likewise.
	* f-lang.c (f_language_data): Likewise.
	* go-lang.c (go_language_data): Likewise.
	* language.c (unk_lang_trampoline): Delete function.
	(skip_language_trampoline): Update.
	(unknown_language_data): Delete skip_trampoline initializer.
	(auto_language_data): Likewise.
	* language.h (language_data): Delete skip_trampoline field.
	(language_defn::skip_trampoline): New function.
	* m2-lang.c (m2_language_data): Delete skip_trampoline
	initializer.
	* objc-lang.c (objc_skip_trampoline): Delete function, move
	implementation to objc_language::skip_trampoline.
	(objc_language_data): Delete skip_trampoline initializer.
	(objc_language::skip_trampoline): New member function with
	implementation from objc_skip_trampoline.
	* opencl-lang.c (opencl_language_data): Delete skip_trampoline
	initializer.
	* p-lang.c (pascal_language_data): Likewise.
	* rust-lang.c (rust_language_data): Likewise.