Use AM_CPPFLAGS instead of INCLUDES.

Newer automake complains about the latter.
Remove calls to AM_PROG_CC_STDC.

This has been replaced by AC_PROG_CC since 2002, and was removed in automake
1.13.
Remove jm_MAINTAINER_MODE, removed in automake 1.13.
Remove mentions of ansi2knr, dropped from auto* in 2011.

(All of these were commented out anyway.)
Use AC_CONFIG_HEADERS instead of AM_CONFIG_HEADER.

The latter has been removed in automake 1.13; the former's been available since
2002.
Use AC_LANG and AC_LANG_PROGRAM in configure tests.

Some tests in ccsp and tranx86 didn't say what language they were in, which
autoconf warns about now; they're now explicitly C.