Depend unit test on existing font.

Commit 734cf8395 introduced a unit test, which depends on a Calibri
metric-compatible font. So this adds a fonctconfig based check to
configure and just runs this test, if configure finds a correctly
mapped font.

Reviewed on:
	https://gerrit.libreoffice.org/7596

Change-Id: I5255a4366684b115d88adca78ab2002864b63766