Fix build failures on Ubuntu 13.10.

Automake now insists that we run AM_PROG_AR if we're going to build a
library, and AM_PROG_CC_C_O if we're going to build anything with
extra compile options. Those extra macros seem harmless in previous
versions of automake.


git-svn-id: svn://svn.tartarus.org/sgt/putty@10053 cda61777-01e9-0310-a592-d414129be87e