Fix thread-unsafe lazy initializations.

Fix thread-unsafe lazy initializations.

* libguile/backtrace.c (print_exception_var): New static variable.
  (init_print_exception_var): New static function.
  (scm_print_exception): Remove thread-unsafe lazy initialization.
  Call 'init_print_exception_var' using 'scm_i_pthread_once'.
  Use 'print_exception_var'.

* libguile/continuations.c (call_cc): New static variable.
  (init_call_cc): New static function.
  (scm_i_call_with_current_continuation): Remove thread-unsafe lazy
  initialization.  Call 'init_call_cc' using 'scm_i_pthread_once'.

* libguile/debug.c (local_eval_var): New static variable.
  (init_local_eval_var): New static function.
  (scm_local_eval): Remove lazy initialization using mutexes.
  Call 'init_local_eval_var' using 'scm_i_pthread_once'.
  Use 'scm_variable_ref' instead of 'SCM_VARIABLE_REF'.

* libguile/eval.c (map_var, for_each_var): New static variables.
  (init_map_var, init_for_each_var): New static functions.
  (scm_map, scm_for_each): Remove thread-unsafe lazy initializations.
  Call 'init_map_var' (or 'init_for_each_var') using 'scm_i_pthread_once'.
  Use 'map_var' (or 'for_each_var').

* libguile/frames.c (frame_arguments_var): New static variable.
  (init_frame_arguments_var): New static function.
  (scm_frame_arguments): Remove thread-unsafe lazy initialization.
  Call 'init_frame_arguments_var' using 'scm_i_pthread_once'.
  Use 'frame_arguments_var'.  Use 'scm_variable_ref' instead of
  'SCM_VARIABLE_REF'.

* libguile/goops.c (delayed_compile_var): New static variable.
  (init_delayed_compile_var): New static function.
  (make_dispatch_procedure): Remove thread-unsafe lazy initialization.
  Call 'init_delayed_compile_var' using 'scm_i_pthread_once'.
  Use 'delayed_compile_var'.  Use 'scm_variable_ref' instead of
  'SCM_VARIABLE_REF'.

* libguile/instructions.c (instructions_by_name): New static variable.
  (init_instructions_by_name): New static function.
  (scm_lookup_instruction_by_name): Remove thread-unsafe lazy
  initialization.  Call 'init_instructions_by_name' using
  'scm_i_pthread_once'.

* libguile/ports.c (current_warning_port_var)
  (current_warning_port_once): New static variables.
  (init_current_warning_port_var): New static function.
  (scm_current_warning_port): Remove lazy initialization using mutexes.
  Call 'init_current_warning_port_var' using 'scm_i_pthread_once'.
  Use 'current_warning_port_var'.
  (scm_set_current_warning_port): Remove thread-unsafe lazy initialization.
  Call 'init_current_warning_port_var' using 'scm_i_pthread_once'.
  Use 'current_warning_port_var'.

* libguile/strings.c (null_stringbuf): New static variable.
  (init_null_stringbuf): New static function.
  (scm_i_make_string): Remove thread-unsafe lazy initialization.
  Call 'init_null_stringbuf' using 'scm_i_pthread_once'.

* libguile/strports.c (eval_string_var, k_module): New static variables.
  (init_eval_string_var_and_k_module): New static function.
  (scm_eval_string_in_module): Remove lazy initialization using mutexes.
  Call 'init_eval_string_var_and_k_module' using 'scm_i_pthread_once'.
  Use 'eval_string_var'.

* libguile/throw.c (CACHE_VAR): Remove incorrect macro.
  (catch_var, throw_var, with_throw_handler_var): New static variables.
  (scm_catch, scm_catch_with_pre_unwind_handler): Remove thread-unsafe
  lazy initialization.  Use 'catch_var'.
  (init_with_throw_handler_var): New static function.
  (scm_with_throw_handler): Remove thread-unsafe lazy initialization.
  Call 'init_with_throw_handler_var' using 'scm_i_pthread_once'.
  Use 'with_throw_handler_var'.
  (scm_throw): Remove thread-unsafe lazy initialization.
  Use 'throw_var'.
  (scm_init_throw): Initialize 'catch_var' and 'throw_var'.