Move to-upper and to-lower to definitions.mk

So they can be used by art/test/Android.run-test.mk.

Also remove the line wrapping, which was inserting extra characters
at the beginning of the result, and add a sanity check.

Bug: 26275726
Test: no change to out/build-hikey960-test-art.ninja
Change-Id: I35b54c258a1dc76bb1a8a758ec4a08915a2b226d