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 r257670:
Modify the libproc breakpoint add/remove functions to stop the target
process if it has not already been stopped, since this is required for
ptrace(2) to work.

libdtrace does not seem to stop target processes before trying to remove
their breakpoints, so we were previously failing to remove the breakpoint
on r_debug_state() in rtld. This was causing processes to die with SIGTRAP
if they called dlopen(3) after dtrace(1) had detached.

MFC r256661 r257222 r257235 r257248 r257298.

MFC r256661:
Fix the libproc build when DEBUG is defined.

MFC r257222:
Clean up the debug printing in libproc a bit. In particular:

* Don't print any error messages to stderr unless DEBUG is defined.
* Add a DPRINTFX macro for use when errno isn't set.
* Print the error string from libelf when appropriate.

MFC r257235:
Remove an incorrect debug printf.

MFC r257248:
Fix the build with gcc.

MFC r257298:
Revert r257248 and fix the problem in a way that doesn't violate style(9).

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

Approved by: re (implicit)

Several fixes for libproc:
o return the correct status in proc_wstatus()
o proc_read takes a void *
o correctly allocate the objs structure array

Sponsored by: The FreeBSD Foundation

New version of libproc. Changes are:
* breakpoint setup support
* register query
* symbol to address mapping and vice-versa
* more misc utility functions based on their Solaris counterpart

Also, I've written some test cases.

Sponsored by: The FreeBSD Foundation