Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r239501:
- Use pid_t type instead of just int.

MFC r239611:
- Put arguments for print_syscall_ret() function in proper order.
Bug was introduced in r192025.

MFC r239898:
- Remove unused variables.
- Fix warnings about comparing signed and unsigned ints.

MFC r240005:
- Style(9) cleanup.

MFC r240364:
- Remove unused variables.
- Remove redundant return after err(3) call.

MFC r240393:
- Fix detaching under some circumstances.

When truss is detaching from very active process it is possible to
hang on waitpid(2) in restore_proc() forever, because
ptrace(PT_SYSCALL) must be called before detaching, to allow the
debugging process to continue execution. Also when truss called with
'-c' argument, it does not print anything after detach, because it
immediately exits from restore_proc().

To fix these two problems make detaching deferred, but then it is
impossible to detach from a process which does not do any system call.
To fix this issue use sigaction(2) instead of signal(3) to disable
SA_RESTART flag for waitpid(2) that makes it non-restartable. Remove
global variable child_pid, because now detaching is handled in context
where child's pid is known.

MFC r240562:
- Make truss thread-aware.

Approved by: kib (mentor)

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

s/sytem/system in comments, no functional changes.

Reviewed by: alfred@

Fix copyright spelling.

PR: 139825
Submitted by: Ruslan Mahmatkhanov

This fix makes it so the args are malloc'd before
we use them (always a good idea ;-0)

This was found and fixed by JC

Obtained from: JC (c.jayachandran@gmail.com)

Correct off-by-one issue in truss(1) which happens when system call number
is nsyscalls.

PR: bin/134916
Submitted by: Steven Hartland <steven hartland multiplay co uk>
MFC after: 2 weeks

Reduce diff against my local version: replace malloc+memset() cases to calloc().

Fix print_syscall_ret parameter order.

Fix compilation error introduced in r192025.

Add preliminary support for truss on MIPS. It compiles, but has not
been extensively tested. And the ELF64 stuff likely is not quite
right...

# There's a lot of cut-n-paste code here that could easily be
# refactored, at least for FreeBSD syscalls.