MFC r257670:

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.

git-svn-id: svn://svn.freebsd.org/base/stable/9@259968 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f