* findvar.c: Include "builtin-regs.h".

* findvar.c: Include "builtin-regs.h".
(value_of_register): Call value_of_builtin_reg when applicable.
* parse.c: Include "builtin-regs.h" and "gdb_assert.h".
(target_map_name_to_register): Call
builtin_reg_map_name_to_regnum.
* Makefile.in (SFILES): Add builtin-regs.c and std-regs.c.
(COMMON_OBS): Add builtin-regs.o and std-regs.o.
(builtin_regs_h): Define.
(builtin-regs.o): New target.
(findvar.o): Add $(builtin_regs_h).
* builtin-regs.c, builtin-regs.h: New files.
* std-regs.c: New file.
Partial fix for PR gdb/251.