Build HarfBuzz with multi-thread support.

Change-Id: I0d0061aaa37c49ca108203df955318f4481db874
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206916
Commit-Queue: Ben Wagner <bungeman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
diff --git a/third_party/harfbuzz/BUILD.gn b/third_party/harfbuzz/BUILD.gn
index e657af0..4718c8c 100644
--- a/third_party/harfbuzz/BUILD.gn
+++ b/third_party/harfbuzz/BUILD.gn
@@ -26,7 +26,6 @@
       "HAVE_ICU",
       "HAVE_ICU_BUILTIN",
       "HAVE_OT",
-      "HB_NO_MT",
     ]
     deps = [
       "//third_party/icu",