If two targets using the same OS are built in parallel,
they can both try to install the same include/os/* file
at the same time, causing the installEpics.pl script to
die. We fix this by making all installations atomic:
First copy the file to the installation directory using
a unique name, then rename it to the target name. The
target name is in the same directory and filesystem as
the temporary name, so the rename should be atomic.
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