Replace PREPARE_VERSION macro with inline function

	* sysdeps/unix/sysv/linux/dl-vdso.h (PREPARE_VERSION): Remove macro.
	(prepare_version_base): New helper inline function.
	(prepare_version): New macro replacing PREPARE_VERSION.
	(PREPARE_VERSION_KNOWN): Use prepare_version instead of PREPARE_VERSION.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>