Allow 'ptype/o' for assembly

PR exp/28359 points out that 'ptype/o' does not work when the current
language is "asm".

I tracked this down to a hard-coded list of languages in typeprint.c.
This patch replaces this list with a method on 'language_defn'
instead.  If all languages are ever updated to have this feature, the
method could be removed; but in the meantime this lets each language
control what happens.

I looked at having each print_type method simply modify the flags
itself, but this doesn't work very well with the feature that disables
method-printing by default (but allows it via a flag).

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28359
Approved-By: Andrew Burgess <aburgess@redhat.com>
Approved-By: Keith Seitz <keiths@redhat.com>

gdb/language.h

@@ -451,6 +451,13 @@ struct language_defn
     return nullptr;
   }
 
+  /* Return true if this class' implementation of print_type can
+     handle the /o modifier.  */
+  virtual bool can_print_type_offsets () const
+  {
+    return false;
+  }
+
   /* Print TYPE to STREAM using syntax appropriate for this language.
      LEVEL is the depth to indent lines by.  VARSTRING, if not NULL or the
      empty string, is the name of a variable and TYPE should be printed in