Ubuntu – How to find out which GCC toolchain is installed

I would like to debug my embedded target with Insight debugger.

The debugging host is Xubuntu 64bit, the debugging target is an ARM Cortex-M4 connected through a JTAG debugger.

According to this website, I can compile Insight for my setup with these commands:

./configure --host=i686-linux-gnu --target=arm-linux-gnueabi --disable-werror  --prefix=/usr
make
make install

Unfortunately, make quits with this error message: /bin/bash: i686-linux-gnu-ar: command not found, altough ar seems to be installed:

manuel@manuel-VirtualBox:~/insight/insight-6.8-1$ ar --version
GNU ar (GNU Binutils for Ubuntu) 2.24
Copyright 2013 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) any later version.
This program has absolutely no warranty.

Questions:

1. How do I find out which toolchain string to provide with configure argument --host?
2. The programs I'm running on the target get compiled using the GNU Tools for ARM Embedded Processors. gcc, ld and so on are prefixed with gcc-arm-none-eabi-. Hence, do I have to change the --target argument to gcc-arm-none-eabi?
3. Because Insight is not installed by the package manager, I'm afraid it messes up the system and is not removable. Hence I would like to install it in my home directory. Is it enough to change --prefix=/usr to --prefix=/home/manuel/usr/local?