Merge libiberty: Initialize d_printing in all cplus_demangle_fill_* functions.

Merge libiberty: Initialize d_printing in all cplus_demangle_fill_* functions.

While integrating the d_printing recursion guard change into gdb I
noticed we forgot to initialize the demangle_component d_printing
field in cplus_demangle_fill_{name,extended_operator,ctor,dtor}.
As is done in cplus_demangle_fill_{component,builtin_type,operator}.
It happened to work because in gcc all demangle_components were
allocated through d_make_empty. But gdb has its own allocation
mechanism (as might other users).

libiberty/ChangeLog:

       * cp-demangle.c (cplus_demangle_fill_name): Initialize
       demangle_component d_printing.
       (cplus_demangle_fill_extended_operator): Likewise.
       (cplus_demangle_fill_ctor): Likewise.
       (cplus_demangle_fill_dtor): Likewise.

gdb/ChangeLog:

       * cp-name-parser.y (make_empty): Initialize d_printing to zero.