libstdc++: Fix required locales of a testcase

The testsuite for libstdc++ aims to skips test cases for which not all
required locales are installed. This patch adds missing directives about
required locales to one test case to avoid false positive test failures
on systems that have a partial set of locales installed.

Verified by test suite runs that this patch changes the test case from
FAIL to UNSUPPORTED when not all required locales are available and that
the test case will run and PASS when the necessary locales have been
added.

libstdc++-v3/ChangeLog:

	* testsuite/22_locale/locale/cons/5.cc: Add missing directives
	for required locales.