harfbuzz test: compile fewer files

TBR=
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1957353002

Review-Url: https://codereview.chromium.org/1957353002
diff --git a/gyp/harfbuzz.gyp b/gyp/harfbuzz.gyp
index ce7b42f..5bdc2be 100644
--- a/gyp/harfbuzz.gyp
+++ b/gyp/harfbuzz.gyp
@@ -17,7 +17,7 @@
         'HB_NO_MT',
       ],
       'sources': [
-        '<!@(python find.py <(hb_directory)/src "*.c*")',
+        '<!@(python find.py <(hb_directory)/src "hb-*.c*")',
       ],
       'sources!': [
         '<(hb_directory)/src/hb-directwrite.cc',