cygwin ld import library issue fix (removing unused "_nm_" symbols)

[Ralf Habacker]

Hi Charles,
>
> (*) tentative because I can't actually test it myself against HEAD,
> given the pre-existing problem with binutils HEAD on pe386.
>
The unwanted symbols, which this patch avoid, seems to be exported in some
packages. When this patch is applied, perhaps it makes sense to update the
following libs.

dll                   count
/bin/cygcrypto.dll     75
/bin/cygexslt-0.dll    106
/bin/cygform6.dll     45
/bin/cyggdbm.dll     25
/bin/cyghistory5.dll     26
/bin/cygintl-1.dll     35
/bin/cygjbig1.dll      9
/bin/cygjpeg6b.dll     17
/bin/cygltdl-3.dll     31
/bin/cygmenu6.dll     34
/bin/cygncurses++6.dll    254
/bin/cygncurses6.dll     74
/bin/cygpanel6.dll     14
/bin/cygpcre.dll     24
/bin/cygpcreposix.dll     26
/bin/cygpng2.dll     28
/bin/cygreadline5.dll     72
/bin/cygregex.dll     42
/bin/cygssl.dll    200
/bin/cygtiff3.dll     65
/bin/cygxml2-2.dll     67
/bin/cygxslt-1.dll    161
/bin/cygxsltbreakpoint-1.dll      9
/bin/cygz.dll     25

Regards

Ralf