drop SkTextBlob alignas(void*), align in Builder manually

GCC can't handle SK_API and alignas() next to each other,
tested up through GCC 8.1.

Instead, just align up the area we allocate for the SkTextBlob.

Bug: skia:8239

Change-Id: Ibdccfc09649b79a6eaa50ffd731d4bab012d24df
Reviewed-on: https://skia-review.googlesource.com/146703
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed