Move D demangling routines out of d-lang.c and into d-support.c, which

Move D demangling routines out of d-lang.c and into d-support.c, which
is intended to house other D language support functions.

gdb/ChangeLog:
2014-01-17  Iain Buclaw  <ibuclaw@gdcproject.org>

    * Makefile.in (SFILES): Add d-support.c.
    (COMMON_OBS): Add d-support.o.
    * d-lang.h (d_parse_symbol): Add comment, now defined in
    d-support.c.
    * d-lang.c (parse_call_convention)
    (parse_attributes, parse_function_types)
    (parse_function_args, parse_type, parse_identifier)
    (call_convention_p, d_parse_symbol): Move functions to ...
    * d-support.c: ... New file.