8194734 : Handle to jimage file inherited into child processes (win)

[Alexander Miloslavskiy]

 > The update to osSupport_Windows.cpp looks okay. I think it would be
 > useful to discuss the osSupport_unix.cpp change further as the
 > childproc code is supported to close the file descriptors.

childproc code uses some dark magic to figure which files to close. At 
the moment, closeDescriptors() will close all files which has 
descriptors bigger then from_fd (4). However, jimage ends up having 
descriptor 3, so it's not closed. On the other hand, childproc expects 
descriptor 3 to be occupied by a pipe to parent (FAIL_FILENO). This 
means that currently, dark magic is already broken. The only reason for 
jimage to not go into child process is being mistaken with FAIL_FILENO.

One way of fixing bug in childproc could be increasing FAIL_FILENO to 
match its actual value of file descriptor. This way, jimage will no 
longer be mistaken with FAIL_FILENO and therefore, it will NOT be closed.

With all this in mind, I believe it wouldn't hurt to explicitly say that 
jimage must not be inherited, without relying on current implementation 
of childproc. That makes a sturdy and clean code.

When this patch is accepted, I can also work on fixing bugs in 
childproc, if that is considered worthy.