Cygwin: add secure_getenv

Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>

winsup/cygwin/environ.cc

@@ -549,6 +549,16 @@ _getenv_r (struct _reent *, const char *name)
   return findenv_func (name, &offset);
 }
 
+/* Like getenv, but returns NULL if effective and real UID/GIDs do not match */
+extern "C" char *
+secure_getenv (const char *name)
+{
+  int offset;
+  if (cygheap->user.issetuid ())
+    return NULL;
+  return findenv_func (name, &offset);
+}
+
 /* Return number of environment entries, including terminating NULL. */
 static int __stdcall
 envsize (const char * const *in_envp)