Originally filed as rust-lang/rust#52693 but as far as I can tell, this is actually cargo's doing:

I was looking at the output of x.py with -vv for $reasons, and noticed that commands run with LD_LIBRARY_PATH set to multiple paths, separated with a colon, which is normal, but the last character is a colon, which effectively adds the current working directory in the list of paths used. This is generally considered bad practice.

FWIW, when LD_LIBRARY_PATH is set before running x.py, its original value ends up at the end of the LD_LIBRARY_PATH that had a trailing colon.

Cc: @alexcrichton