Launch QEMU with sysroot if specified

[gsingh93]

When launching an ARM binary with QEMU using gdb.debug, we need to specify the -L flag to tell QEMU where the sysroot is. Otherwise it will use the default system root instead of the one we specified.

I tested this with the following code before and after this change:

#!/usr/bin/env python2

from pwn import *

context(arch='arm')
p = gdb.debug('./nightmare', sysroot='./')
p.interactive()

Afterwards, I could see that the loaded libraries in vmmap were from the correct sysroot.

[zachriggle]

@gsingh93 can you double-check that my change (should be cosmetic only) still works for your use-case?

[gsingh93]

@zachriggle no, qemu_user is missing from the qemu_args array on line 432. We also need to add add this flag along with the -g flag, which was why in my commit I'm appending the original arguments (containing the -g flag) after I added the -L flag.

[gsingh93]

ping @zachriggle

[zachriggle]

Looks like we discard the previous QEMU args this way?