(pushdecl): Internally generated vars can be
detected with DECL_SOURCE_LINE of zero, not DECL_IGNORED_P.

(start_enum): Push obstacks, switch to permanent if global.
(finish_enum): Pop obstacks.
(store_parm_decls): When clearing ->names, clear out the values
from the identifiers, restore shadowed values, and clear ->shadowed.

(grokdeclarator): Don't warn of const or volatile function
in a system header file.
(start_struct): Push the obstacks.
Switch to permanent if at top level.
(finish_struct): Pop them.

(store_parm_decls): If we have (erroneously) a prototype
and old-style parm decls, throw away the old-style parm decls.
(finish_decl): Do the pop_obstacks sooner, when it's
time to start allocating in the ambient context's obstack.
Don't call permanent_allocation unless got back to permanent obstack.

(explicit_flag_signed_bitfields): New variable.
(c_decode_option): Set that for -f[un]signed-bitfields.
(grokdeclarator): If that's set, and -fsigned-bitfields,
disregard -traditional when handling bitfield signedness.

From-SVN: r2332