Mark function used as template parameter extern.

VC++19.10.2517 does not support the C++11 change to allow the address of
internal linkage objects to be used as non-type template arguments.

BUG=skia:6351

Change-Id: I7e1f628db794f950dfba7d043cf6d2fbf0a8c453
Reviewed-on: https://skia-review.googlesource.com/9496
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index eee76d5..d155308 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -388,7 +388,8 @@
 }
 
 // Caller must lock gFTMutex before calling this function.
-static void unref_ft_face(SkFaceRec* faceRec) {
+// Marked extern because vc++ does not support internal linkage template parameters.
+extern /*static*/ void unref_ft_face(SkFaceRec* faceRec) {
     gFTMutex.assertHeld();
 
     SkFaceRec*  rec = gFaceRecHead;