This patch adds a file posix-conf-vars.list that is used to generate
macros to determine if a macro is defined as set, unset or not
defined. gen-posix-conf-vars.awk processes this file and generates a
header (posix-conf-vars-def.h) with these macros. A new header
posix-conf-vars.h includes this generated header and defines accessor
macros for the generated macros.
Tested on x86_64.
* posix/Makefile (before-compile): Add posix-conf-vars-def.h.
($(objpfx)posix-conf-vars-def.h): New target.
* posix/posix-conf-vars.list: New file.
* posix/posix-conf-vars.h: New file.
* posix/confstr.c: Include posix-conf-vars.h.
(confstr): Use CONF_IS_* macros.
* posix/posix-envs.def: Include posix-conf-vars.h. Use
CONF_IS_* macros.
* scripts/gen-posix-conf-vars.awk: New file.
