poco: fix m68k compile

Add a patch from double-conversion upstream project which is bundled
with poco to fix compile for m68k.

Fixes:
  http://autobuild.buildroot.net/results/791917c1343f53e12f27b06cfd5e1d2e88078014/
  http://autobuild.buildroot.net/results/349d4b49d65a652551c4de20233684bb4ffa5ae3/



Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>