The common igen code was forked from the ppc long ago. The lf module
is still pretty similar in API, so we can unfork them with a little
bit of effort.
Some of the generated ppc code is now slightly different, but that's
because of fixes the common igen code has gained, but not the ppc igen
code (e.g. fixing of #line numbers).
The ppc code retains lf_print__c_code because the common igen code
rewrote the logic to a new table.c API. Let's delay that in the ppc
code to at least unfork all this code.
Since we require C11 now, we can assume many headers exist, and
clean up all of the conditional includes. It's not like any of
this code actually accounted for the headers not existing, just
whether we could include them.
The strings.h cleanup is a little nuanced: it isn't in C11, but
every use of it in the codebase will include strings.h only if
string.h doesn't exist. Since we now assume the C11 string.h
exists, we'll never include strings.h, so we can delete it.
