Fix bug in cooked index scanner

Testing this entire series pointed out that the cooked index scanner
disagrees with new_symbol about certain symbols.  In particular,
new_symbol has this comment:

    Ada and Fortran subprograms, whether marked external or
    not, are always stored as a global symbol, because we want

This patch updates the scanner to match.

I don't know why the current code does not cause failures.

It's maybe worth noting that incremental CU expansion -- creating
symtabs directly from the index -- would eliminate this sort of bug.

gdb/dwarf2/read.c

@@ -16326,6 +16326,12 @@ cooked_indexer::scan_attributes (dwarf2_per_cu_data *scanning_per_cu,
 	      || abbrev->tag == DW_TAG_enumeration_type
 	      || abbrev->tag == DW_TAG_enumerator))
 	*flags &= ~IS_STATIC;
+
+      /* Keep in sync with new_symbol.  */
+      if (abbrev->tag == DW_TAG_subprogram
+	  && (m_language == language_ada
+	      || m_language == language_fortran))
+	*flags &= ~IS_STATIC;
     }
 
   return info_ptr;