Use posix-conf-vars.list to generate spec array

This patch adds support to generate the spec array in getconf from the
conf.list.  The generated code is mostly unchanged.  the only changes
are due to the change in layout of the spec and val arrays in the ELF.

The val array can also be auto-generated from posix-conf-vars.list
once the remaining macros are added to it.

	* posix/posix-conf-vars.list (SPEC:XBS5): Add sysconf prefix.
	* posix/confstr.c: Define NEED_SPEC_ARRAY to 0.
	* posix/posix-envs.def: Likewise.
	* sysdeps/posix/sysconf.c: Likewise.
	* posix/getconf.c: Define NEED_SPEC_ARRAY to 1.
	(specs): Remove array.
	* scripts/gen-posix-conf-vars.awk: Support generation of specs
	array.