gdb: Convert language la_sniff_from_mangled_name field to a method

gdb: Convert language la_sniff_from_mangled_name field to a method

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

Previously the la_sniff_from_mangled_name pointer was NULL for some
languages, however, all uses of this function pointer were through the
function language_sniff_from_mangled_name which provided a default
implementation.

This default implementation now becomes the implementation in the base
class language_defn, which is then overridden as required in various
language sub-classes.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* ada-lang.c (ada_sniff_from_mangled_name): Delete function,
	implementation moves to...
	(ada_language::sniff_from_mangled_name): ...here.  Update return
	type.
	(ada_language_data): Delete la_sniff_from_mangled_name
	initializer.
	* c-lang.c (c_language_data): Likewise.
	(cplus_language_data): Likewise.
	(cplus_language::sniff_from_mangled_name): New member function,
	implementation taken from gdb_sniff_from_mangled_name.
	(asm_language_data): Delete la_sniff_from_mangled_name
	initializer.
	(minimal_language_data): Likewise.
	* cp-support.c (gdb_sniff_from_mangled_name): Delete,
	implementation moves to cplus_language::sniff_from_mangled_name.
	* cp-support.h (gdb_sniff_from_mangled_name): Delete declaration.
	* d-lang.c (d_sniff_from_mangled_name): Delete, implementation
	moves to...
	(d_language::sniff_from_mangled_name): ...here.
	(d_language_data): Delete la_sniff_from_mangled_name initializer.
	* f-lang.c (f_language_data): Likewise.
	* go-lang.c (go_sniff_from_mangled_name): Delete, implementation
	moves to...
	(go_language::sniff_from_mangled_name): ...here.
	(go_language_data): Delete la_sniff_from_mangled_name initializer.
	* language.c (language_sniff_from_mangled_name): Delete.
	(unknown_language_data): Delete la_sniff_from_mangled_name
	initializer.
	(auto_language_data): Likewise.
	* language.h (language_data): Delete la_sniff_from_mangled_name
	field.
	(language_defn::sniff_from_mangled_name): New function.
	(language_sniff_from_mangled_name): Delete declaration.
	* m2-lang.c (m2_language_data): Delete la_sniff_from_mangled_name
	field.
	* objc-lang.c (objc_sniff_from_mangled_name): Delete,
	implementation moves to...
	(objc_language::sniff_from_mangled_name): ...here.
	(objc_language_data): Delete la_sniff_from_mangled_name initializer.
	* opencl-lang.c (opencl_language_data): Likewise.
	* p-lang.c (pascal_language_data): Likewise.
	* rust-lang.c (rust_sniff_from_mangled_name): Delete,
	implementation moves to...
	(rust_language::sniff_from_mangled_name): ...here.
	(rust_language_data): Delete la_sniff_from_mangled_name
	initializer.
	* symtab.c (symbol_find_demangled_name): Call
	sniff_from_mangled_name member function.