Revert of SK_DECLARE_STATIC_MUTEX -> static SkMutex

src/ports/SkFontConfigInterface_direct.cpp

Index: src/ports/SkFontConfigInterface_direct.cpp
diff --git a/src/ports/SkFontConfigInterface_direct.cpp b/src/ports/SkFontConfigInterface_direct.cpp
index f2360020ad9a585c5b0c61678511357bad630556..d6fa96a46cfa5c418516a860edbfc9af9937a385 100644
--- a/src/ports/SkFontConfigInterface_direct.cpp
+++ b/src/ports/SkFontConfigInterface_direct.cpp
@@ -32,7 +32,7 @@
 
 // Fontconfig is not threadsafe before 2.10.91. Before that, we lock with a global mutex.
 // See https://bug.skia.org/1497 for background.
-static SkMutex gFCMutex;
+SK_DECLARE_STATIC_MUTEX(gFCMutex);
 
 #ifdef SK_DEBUG
 void* CreateThreadFcLocked() { return new bool(false); }