Fix posix/tst-glob_lstat_compat on alpha [BZ #22818]

Fix posix/tst-glob_lstat_compat on alpha [BZ #22818]

The tst-glob_lstat_compat test needs to run tests on the previous
version of glob. On alpha, there are three versions of glob, GLIBC_2.0,
GLIBC_2.1 and GLIBC_2.27, while on other architectures there are only
the GLIBC_2.0 and GLIBC_2.27 version. Therefore on alpha the previous
version is GLIBC_2.1 and not GLIBC_2.0.

Changelog:
	[BZ #22818]
	* posix/tst-glob_lstat_compat.c [__alpha__] (glob): Access
	the GLIBC_2.1 version.