precompiled headers and cygwin

[JJ]

Is there a special trick to making precompiled headers work under CygWin?

I had read and followed the directions, but on testing I find that the 
.h file is always used and the .h.gch is never used. These are the 
directions I followed. The following directions are on the web but are 
the same as the ones on my hard disk for my CygWin version of g++.

http://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html#Precompiled%20Headers

Here's the general idea of how I tested it in pseudo code. (I just typed 
the following from scratch without running it so it probably has typos 
When I did the test, I didn't actually use a DOS batch file and I don't 
actually have a program called 'replace.exe.' <G> I also didn't have any 
comments in any of the files.)

======= example =======

//---------------------
// file: pre.h

#include <iostream>

const int a = 4;

//---------------------
// file: main.cpp

#include pre.h

using namespace std;

int main(){
  cout << a << endl;
}

#----------------------
# file: makefile

main : main.o pre.h.gch
        g++ main.o -o main

main.o : main.cpp pre.h
        g++ -c main.cpp -o main.o

:gch
        g++ -x c++ -c pre.h -o pre.h.gch

rem--------------------
rem file: test.bat

rem Update precompiled header and make.
make gch
make

rem prints 4
main

rem Edits pre.h to assign '2' to 'a.'
replace "pre.h" "4" "2"

rem Make without updating precompiled header.
make

rem Prints 4 if precompiled headers are working
rem or 2 if they are not working.
main

====== end example ======

When I run 'test,' it always prints 4 then 4 for me.
If precompiled headers were working, I would get 4
then 2.

Jeff