Ruby

When attempted to use FD_SETSIZE preprocesor definition under Windows to increase number of file descriptions, found that configure script replicated it.

A simple configure invoke with `sh configure --enable-shared CPPFLAGS='-DFD_SETSIZE=32767' result in the following value returned by RbConfig:

irb(main):001:0> require "rbconfig"
=> false
irb(main):002:0> RbConfig::CONFIG["CPPFLAGS"]
=> "-DFD_SETSIZE=32767  -DFD_SETSIZE=32767"

Above is result from Ruby 1.9.3, and for ruby-trunk:

irb(main):001:0> require "rbconfig"
=> false
irb(main):002:0> RbConfig::CONFIG["CPPFLAGS"]
=> "-DFD_SETSIZE=32767 -D_WIN32_WINNT=0x0501 -DFD_SETSIZE=32767"

I'm not very versed on configure.in, so can't find the culprit of this duplication, sorry about that.