autoheader, automake, autoconf

Some notes about these wonderful tools.

• When incorporating and distributing third-party source code, autoconf can bootstrap recursively the third-party configure script. Specify using AC_CONFIG_SUBDIRS([third_party/src/...]). Additional configure arguments for the recursive invocation can be added to $ac_configure_args right before AC_OUTPUT.
• Modernized configure.ac uses AC_INIT([name], [version], [desc]). To add automake capability, just use AM_INIT_AUTOMAKE without arguments.
• Autoheader is used to generate config.h.in from configure.ac, which derives the configure script that converts config.h.in to config.h. The config.h file contains C preprocessor macros that affect compilation behavior depending on the outcome of configure script. Autoheader either requires AC_DEFINE to provide a description (third argument) or AH_TEMPLATE([VAR_NAME], [desc]) to exist in configure.ac.
• To check for packages using pkg-config, use PKG_CHECK_MODULES(VARIABLE-PREFIX, MODULES, [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND]) macro (pkg.m4 seems to be the only source of documentation). If [ACTION-IF-NOT-FOUND] is blank, then the default is to fail and quit configure script. Supply [true] to make this package optional (i.e. if package not present, continue gracefully).