Include IceCC's compilerwrapper binary

[aperezdc]

From compilerwrapper.cpp:

/*
Older icecream versions assume the compiler is always GCC. This can
be fixed on the local side, but remote nodes would need icecream upgrade.
As a workaround icecc-create-env includes this wrapper binary in the environment
if clang is to be used as well, that will either call clang or the real gcc.
Which one depends on an extra argument added by icecream.
*/

While not strictly needed with newer version of IceCC, it would be good to include it in the same way as icecc-create-env does to ensure compatibility of the generated tarballs with older IceCC versions.

[aperezdc]

One way to go about this would be:

• Optionally supporting a configuration directory at $XDG_CONFIG_HOME/popsicle. If there is a compilerwrapper symlink inside it, it will be assumed to point to the corresponding binary provided by IceCC.
• If the configuration directory does not exist, or there is no compilerwrapper symlink, or it points to a non-existing file, then support for adding it into generated tarballs is disabled.