Build fails on cygwin x86_64 system

[Havasi Gábor]

In a x86_64-pc-cygwin (Windows) system - compiler is gcc 3.4.1 - after

  export CFLAGS="-O2"
  ./configure

the make fails with the message

  /bin/sh ../libtool --mode=compile 
gcc -DHAVE_CONFIG_H -I. -I. -I.. -D__GMP_WITHIN_GMP -I.. -DOPERATION_`echo 
mul_fft | sed 's/_$//'`    -O2 -c -o mul_fft.lo `test -f mul_fft.c || echo 
'./'`mul_fft.c
  gcc -DHAVE_CONFIG_H -I. -I. -I.. -D__GMP_WITHIN_GMP -I.. -DOPERATION_mul_fft 
 -O2 -c mul_fft.c -o mul_fft.o
  mul_fft.c: In function `mpn_fft_mul_2exp_modF':
  mul_fft.c:168: error: parse error before "LSYM_PREFIX"
  mul_fft.c:168: error: parse error before "LSYM_PREFIX"
  mul_fft.c: In function `mpn_fft_add_modF':
  mul_fft.c:183: error: parse error before "LSYM_PREFIX"
  mul_fft.c:183: error: parse error before "LSYM_PREFIX"
  make[2]: *** [mul_fft.lo] Error 1

The mpn_incr_u and mpn_decr_u macros cause the compile errors.

However, if I call

  export MPN_PATH="generic"

before ./configure, it compiles without any error. In the first case, the 
MPN_PATH variable was "x86_64 generic", set by the program configure. This 
bug seems to be the same as alokgs at cdacb.ernet.in  writes in 
http://gmplib.org/list-archives/gmp-discuss/2005-February/001500.html .
The strange thing that I don't see any difference between calling the 
configure with MPN_PATH = "x86_64 generic" or MPN_PATH = "generic".

Any idea?