strace --quiet: be *really* quiet

The biggest problem with strace spitting out `create_child: ...` despite
being asked to be real quiet is that its output can very well interfere
with scripts' operations.

For example, when running any of Git for Windows' shell scripts with
`GIT_STRACE_COMMANDS=/path/to/logfile` (which is sadly an often needed
debugging technique while trying to address the many MSYS2 issues Git for
Windows faces), any time the output of any command is redirected into a
variable, it will include that `create_child: ...` line, wreaking havoc
with Git's expectations.

So let's just really be quiet when we're asked to be quiet.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

winsup/utils/mingw/strace.cc

@@ -352,7 +352,8 @@ create_child (char **argv)
     flags |= CREATE_NEW_CONSOLE | CREATE_NEW_PROCESS_GROUP;
 
   make_command_line (one_line, argv);
-  printf ("create_child: %s\n", one_line.buf);
+  if (!quiet)
+    printf ("create_child: %s\n", one_line.buf);
 
   SetConsoleCtrlHandler (NULL, 0);
 /* Commit message for this code was: