The find_realexec_path function was used for finding the toolchain path mostly
because of two reasons:
1) We couldn't really use CXX or CC variables because the user could set those
from the OS's environment and Waf wouldn't look for the executable file in
that case.
2) Our CI configuration sets up symlinks for ccache and find_realexec_path
works around that issue.
The bad side about using find_realexec_path() is that, besides working aroung
symlinks, it does the same thing that is done by Waf. This patch removes the
dependency for such a function by addressing each of the reasons above stated:
1) We create a local copy of os.environ and, if there's a variable with the
same name we are using, we remove it from the local copy.
2) As done before, we are looking for the cross ar program instead of gcc
program, since that is not used for ccache symlinks.
1b6a87d8b4