strace.c: replace if (debug_flag) ... with suitable debug printing macros

strace.c: replace if (debug_flag) ... with suitable debug printing macros

* strace.c (alloc_tcb, droptcb, detach, attach_tcb, test_ptrace_seize,
init, startup_tcb): Replace if (debug_flag) error_msg(...) occurrences
with debug_error_msg(...).
(attach_tcb): Replace if (debug_flag) perror_msg(...) with
debug_perror_msg(...).
(cleanup, startup_tcb): Replace if (debug_flag) error_msg(...)
occurrences with debug_func_msg() in attempt to provide additional
information.