c.opt: Introduce -fworking-directory.

c.opt: Introduce -fworking-directory.

* c.opt: Introduce -fworking-directory.
* doc/cpp.texi, doc/invoke.texi, doc/cppopts.texi: Document it.
* c-common.h (flag_working_directory): Declare.
* c-common.c (flag_working_directory): Define.
* c-opts.c (c_common_handle_options): Set it.
(sanitize_cpp_opts): Set...
* cpplib.h (struct cpp_options): ... working_directory option.
(struct cpp_callbacks): Add dir_change.
* cppinit.c (read_original_filename): Call...
(read_original_directory): New.  Look for # 1 "directory//"
and process it.
(cpp_read_main_file): Call dir_change callback if working_directory
option is set.
* gcc.c (cpp_unique_options): Pass -g*.
* c-lex.c (cb_dir_change): New.
(init_c_lex): Set dir_change callback.
* toplev.c (src_pwd): New static variable.
(set_src_pwd, get_src_pwd): New functions.
* toplev.h (get_src_pwd, set_src_pwd): Declare.
* dbxout.c (dbxout_init): Call get_src_pwd() instead of getpwd().
* dwarf2out.c (gen_compile_unit_die): Likewise.
* dwarfout.c (output_compile_unit_die, dwarfout_init): Likewise.

From-SVN: r70189