std.cfg: Add support for snprintf_s().

sprintf_s works very similar but it is already configured in the
windows library. Configuring sprintf_s in std.cfg leads to conflicts in
the windows configuration tests.
Found by daca@home

cfg/std.cfg

@@ -5787,6 +5787,28 @@ The obsolete function 'gets' is called. With 'gets' you'll get a buffer overrun
       <not-uninit/>
     </arg>
   </function>
+  <!-- int sprintf_s(char *restrict buffer, rsize_t bufsz, const char *restrict format, ...); // since C11 // TODO: conflicts with the Windows functions where it is overloaded for C++ also -->
+  <!-- int snprintf_s(char *restrict buffer, rsize_t bufsz, const char *restrict format, ...); // since C11 -->
+  <function name="snprintf_s">
+    <returnValue type="int"/>
+    <noreturn>false</noreturn>
+    <leak-ignore/>
+    <arg nr="1" direction="out">
+      <not-uninit/>
+      <minsize type="argvalue" arg="2"/>
+    </arg>
+    <arg nr="2" direction="in">
+      <not-uninit/>
+      <valid>0:</valid>
+    </arg>
+    <formatstr/>
+    <arg nr="3" direction="in">
+      <formatstr/>
+      <not-null/>
+      <not-uninit/>
+      <strz/>
+    </arg>
+  </function>
   <!-- int swprintf(wchar_t *s, size_t n, const wchar_t *format, ...); -->
   <function name="swprintf,std::swprintf">
     <returnValue type="int"/>