Fix posix/tst-regex by using a dedicated input-file.

The recent commit e6855a3b
changed the encoding of ChangeLog.old/ChangeLog.8 from ISO-8859 to UTF-8.
Unfortunately the test posix/tst-regex assumes the former encoding.
Furthermore Francesco Potortì is now written with 'ì' instead of 'i`'
which would lead to two further matches in the first call to test_expr.

This patch just copies the former ChangeLog.8 file to tst-regex.input
and adjusts the test in order to use this new input file.

ChangeLog:

	* posix/tst-regex.c (do_test): Use tst-regex.input as input file.
	* posix/tst-regex.input: New file.