[freetype2] enable fsanitize=function

Bug: https://fxbug.dev/42078767
Change-Id: Idc962668685b060a4b5e8dce74f4b7be0e57c105
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/freetype2/+/1189312
Reviewed-by: Gulfem Savrun Yeniceri <gulfem@google.com>
Reviewed-by: Daniel Thornburgh <dthorn@google.com>