Cygwin: fork: add PROCESS_VM_OPERATION to child process permissions

...on parent process.  This is required for successful mmap propagation.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/release/3.0.1

@@ -0,0 +1,13 @@
+What's new:
+-----------
+
+
+What changed:
+-------------
+
+
+Bug Fixes
+---------
+
+- Relax fork child permissions to avoid a potential fork failure.
+  Addresses: https://cygwin.com/ml/cygwin/2019-02/msg00234.html

winsup/cygwin/sigproc.cc

@@ -815,7 +815,7 @@ child_info::child_info (unsigned in_cb, child_info_types chtype,
      we're forking, we also need handle duplicate access. */
   parent = NULL;
   DWORD perms = PROCESS_QUERY_LIMITED_INFORMATION | PROCESS_VM_READ
-		| SYNCHRONIZE;
+		| PROCESS_VM_OPERATION | SYNCHRONIZE;
   if (type == _CH_FORK)
     {
       perms |= PROCESS_DUP_HANDLE;