Set the legacy process name with prctl() on assignment to $0 on Linux

Set the legacy process name with prctl() on assignment to $0 on Linux

Ever since perl 4.000 we've only set the POSIX process name via
argv[0]. Unfortunately on Linux the POSIX name isn't used by utilities
like top(1), ps(1) and killall(1).

Now when we set C<$0 = "hello"> both C<qx[ps h $$]> (POSIX) and
C<qx[ps hc $$]> (legacy) will say "hello", instead of the latter being
"perl" as was previously the case.

See also the March 9 2010 thread "Why doesn't assignment to $0 on
Linux also call prctl()?" on perl5-porters.