Bug 12669

I found a bug in FreeBSB with an old perl script that sets 
$SIG{"CHLD"}="IGNORE".  It seems to have broke ever since
SA_NOCLDWAIT has been implemented.  The issue seems that
SA_NOCLDWAIT should be reset after exec so some /bin/sh commands
then hang.  This is was Solaris apparently does so everything
works fine on Solaris even with pthread.

Note this is still broken for libc_r, however, on Solaris 
it works fine with pthreads.  I will investigate that later.

How-To-Repeat: Sample bug:
	perl -e '$SIG{"CHLD"}="IGNORE"; system ("echo hello | echo hang");'

C version:
begin 664 bug.tgz
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end


Machine without patch for resetting SA_NOCLDWAIT after exec.
  770z% gmake 
  rm -f tst tst2
  gmake tst
  gmake[1]: Entering directory `/usr/home/ambrisko'
  gcc     tst.c   -o tst
  gmake[1]: Leaving directory `/usr/home/ambrisko'
  gmake tst2
  gmake[1]: Entering directory `/usr/home/ambrisko'
  gcc     tst2.c   -o tst2
  gmake[1]: Leaving directory `/usr/home/ambrisko'
  ./tst
  Parent change SA_NOCLDWAIT       988       20       22        0
  Parent before SA_NOCLDWAIT       988        0        2        0
  Child before exec SA_NOCLDWAIT   988       20       22        0
  Parent after fork SA_NOCLDWAIT   988       20       22        0
  Start 'system ./tst2'
          Child SA_NOCLDWAIT       991       20       22        0
		[Then hangs]

Machine with patch for resetting SA_NOCLDWAIT after exec.
  dhcp2% make
  rm -f tst tst2
  make tst
  gcc -O -pipe  tst.c  -o tst
  make tst2
  gcc -O -pipe  tst2.c  -o tst2
  ./tst
  Parent change SA_NOCLDWAIT       284       20       22        0
  Parent before SA_NOCLDWAIT       284        0        2        0
  Child before exec SA_NOCLDWAIT   284       20       22        0
  Parent after fork SA_NOCLDWAIT   284       20       22        0
  Start 'system ./tst2'
          Child SA_NOCLDWAIT       287        0        2        0
  Done 'system'
  dhcp2% 

On Solaris 5.7
  % make
  rm -f tst tst2
  make tst
  make[1]: Entering directory `/a/207.76.205.244/root/usr/home/ambrisko'
  gcc     tst.c   -o tst
  make[1]: Leaving directory `/a/207.76.205.244/root/usr/home/ambrisko'
  make tst2
  make[1]: Entering directory `/a/207.76.205.244/root/usr/home/ambrisko'
  gcc     tst2.c   -o tst2
  make[1]: Leaving directory `/a/207.76.205.244/root/usr/home/ambrisko'
  ./tst
  Parent change SA_NOCLDWAIT       26241    10000    10004 effffb30
  Parent before SA_NOCLDWAIT       26241        0    20000 effffb30
  Child before exec SA_NOCLDWAIT   26241    10000    10000 effffb30
  Parent after fork SA_NOCLDWAIT   26241    10000    10000 effffb30
  Start 'system ./tst2'
          Child SA_NOCLDWAIT       26244        0    20000 effffb38
  Done 'system'
  %