[ARM, sim] Fix build failure with -Werror (PR26365)

[ARM, sim] Fix build failure with -Werror (PR26365)

There is a bit of a situation in the ARM sim with regards to the handling
of argv. sim_open () gets a const char **argv, but ARM's sim_open gets
clever and decides to modify argv in place via sim_target_parse_command_line.
I'm not sure why.

In any case, here's a fix that makes the code modify a copy of argv instead.

sim/arm/ChangeLog:

2020-08-13  Luis Machado  <luis.machado@linaro.org>

	PR sim/26365

	* wrapper.c (sim_target_parse_command_line): Free discarded argv
	entries.
	(sim_open): Use a duplicate of argv instead of the original argv.