These are configuration files for various features as detected by configure.
Include only those files you need (in order to reduce rebuilds when a setting changes).
Settings here are only C/C++ #define directives, so they apply only to C/C++ source,
not to Makefiles.
Adding a new setting:
=====================
- do AC_DEFINE(HAVE_FOO) in configure.ac when a setting should be set
- choose the proper config/config_xxx.h file to use
- if it is a global setting (such as availability of a compiler feature),
use config/config_global.h
- otherwise check if there is a matching config/config_hxx.h file
- if none matches, add a new one:
- add config/config_xxx.h.in here, with just #ifndef include guard
- add AC_CONFIG_HEADERS([config/config_xxx.h]) next to the others
in configure.ac
- add config_hxx.h to config/.gitignore
- add #undef HAVE_FOO to the config/config_hxx.h , possibly with a comment
- add #include <config_xxx.h> before any #ifdef HAVE_XXX in a source file
