This commit makes `revamb` produce a new file `.ll.need.csv` containing
a list of all the dynamic libraries required by the input program. This
will be transformed by the 'csv-to-ld-options` (was:
`li-csv-to-ld-options`) into the appropriate linking options.
Update `GeneratedIRReference.rst:` to reflect recent changes to the
`root` function. Specifically, the presence of the stack pointer
argument and initialization of the program counter and the stack
pointer.
`FromIRToExecutable.rst` has been updated too, to take into account the
new way we link `support.c`.
Finally, the `--tracing` argument has been removed from
`RevambUsage.rst` and the `-trace` argument is no documented in
`TranslateUsage.rst`.
Alessandro Di Federico