corrective fix for MinGW GNU C99 printf compliance

Compilation on cygwin, using gcc v3 with option -mno-cygwin,
currently produces a large number of the following warnings:

   warning: `gnu_printf' is an unrecognized format function type

These have been introduced with the recent MinGW GNU C99 printf
compliance patch, as gnu_printf was only introduced with gcc v4.4
and is not recognized with earlier versions.

The attached fix adds gcc version detection to the previous patch
to avoid the problem.