CUDA: Implement nvcc implicit link line extraction more robustly

Do not assume that the implicit link line is the last line of the output
from `nvcc -v`.  Instead first find the `LIBRARIES=` line, and then look
for that content on a later line.  It appears twice.  First on a call to
`nvlink`, which we ignore.  Later it appears on the implicit link line.
Extract the latter line.  On failure, abort with a `FATAL_ERROR` so that
the user does not try to build without proper link information.

Once we have the line, parse it with `separate_arguments` using the
`UNIX_COMMAND` option just like `CMakeParseImplicitLinkInfo` already
does.  This robustly parses the command line and removes quoting.
Then extract the first argument as the host link launcher.