sim/rx: move some variable declarations to the start of the block

sim/rx: move some variable declarations to the start of the block

For sim code variables still need to be declared at the start of the
enclosing block.  This silences a few GCC warnings.

sim/rx/ChangeLog:

	* syscalls.c (rx_syscall): Move declaration of some variables to
	the start of the enclosing block.
	* trace.c (load_file_and_line): Likewise.