cpplib problems

[Dave Brolley]

Hi,

This patch addresses some problems found with the --enable-c-cpplib
compilers. Specifically, cpplib was not getting initialized unless a
language-specific option was specified on the compile. To fix this, I
moved the initialization of cpplib from lang_decode_option to
lang_init_options. I don't know why I put it in lang_decode_option in
the first place. The changes affect the C, C++ and objective C
compilers.

Dave