Move logic out of symbol_find_demangled_name

This patch moves most of the demangling logic out of
symbol_find_demangled_name into the various language_defn objects.

The simplest way to do this seemed to be to add a new method to
language_defn.  This is shame given the existing la_demangle, but
given Ada's unusual needs, and the differing demangling options
between languages, la_demangle didn't seem to fit.

In order to make this work, I made enum language order-sensitive.
This helps preserve the current ordering of demangling operations.

2016-06-23  Tom Tromey  <tom@tromey.com>

	* symtab.c (symbol_find_demangled_name): Loop over languages and
	use language_sniff_from_mangled_name.
	* rust-lang.c (rust_sniff_from_mangled_name): New function.
	(rust_language_defn): Update.
	* p-lang.c (pascal_language_defn): Update.
	* opencl-lang.c (opencl_language_defn): Update.
	* objc-lang.c (objc_sniff_from_mangled_name): New function.
	(objc_language_defn): Update.
	* m2-lang.c (m2_language_defn): Update.
	* language.h (struct language_defn) <la_sniff_from_mangled_name>: New
	field.
	(language_sniff_from_mangled_name): Declare.
	* language.c (language_sniff_from_mangled_name): New function.
	(unknown_language_defn, auto_language_defn, local_language_defn):
	Update.
	* jv-lang.c (java_sniff_from_mangled_name): New function.
	(java_language_defn): Use it.
	* go-lang.c (go_sniff_from_mangled_name): New function.
	(go_language_defn): Use it.
	* f-lang.c (f_language_defn): Update.
	* defs.h (enum language): Reorder.
	* d-lang.c (d_sniff_from_mangled_name): New function.
	(d_language_defn): Use it.
	* cp-support.h (gdb_sniff_from_mangled_name): Declare.
	* cp-support.c (gdb_sniff_from_mangled_name): New function.
	* c-lang.c (c_language_defn, cplus_language_defn)
	(asm_language_defn, minimal_language_defn): Update.
	* ada-lang.c (ada_sniff_from_mangled_name): New function.
	(ada_language_defn): Use it.

gdb/m2-lang.c

@@ -381,6 +381,7 @@ const struct language_defn m2_language_defn =
   basic_lookup_symbol_nonlocal,	/* lookup_symbol_nonlocal */
   basic_lookup_transparent_type,/* lookup_transparent_type */
   NULL,				/* Language specific symbol demangler */
+  NULL,
   NULL,				/* Language specific
 				   class_name_from_physname */
   m2_op_print_tab,		/* expression operators for printing */