package/putty: fix build with uClibc

Add patches fixing a number of build issues with uClibc. The issue fixed
in patch #2 has been reported upstream. Patch #3 has been suggested by
upstream but not applied yet.

Drop the _SUBDIR assignment. The configure script moved to top level
directory since upstream commit a947c49bec3 from 2014. This allows
AUTORECONF to find configure.ac.

Fixes:
http://autobuild.buildroot.net/results/801/801e2b2909363b5dcd9735362bb921e017569edc/
http://autobuild.buildroot.net/results/398/3984c6cdd3398645c8ad98bbe23af9090cf4bfcf/
http://autobuild.buildroot.net/results/632/632f93046f9cceffd9b604911542426c10967e0f/



Cc: Alexander Dahl <post@lespocky.de>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>