Disable HarfBuzz's fallback to compatibility decompositions

Previously, HarfBuzz's default fallback to compatibility
decompositions resulted in Mathematical Alphanumeric Symbols getting
rendered as normal letters and digits when there was no font
available to render them. This patch disables that fallback, to
ensure they are displayed as tofus.

Based on a patch by Behdad Esfahbod.

Bug: 19202569
Change-Id: I357f172302448d4ab0b24efc86119f1977b5996b
1 file changed
tree: 5549dd28346f84152e447a168fc8f7e73e45aa3e
  1. include/
  2. libs/
  3. sample/