Don't require -DSK_USE_POSIX_THREADS.

gyp/common_conditions.gypi

Index: gyp/common_conditions.gypi
diff --git a/gyp/common_conditions.gypi b/gyp/common_conditions.gypi
index 32335f9416e25fa0f7b586ee6895cbd86538fad6..0fbeb09c7840f2ba60d9f425d23146c9cd02935c 100644
--- a/gyp/common_conditions.gypi
+++ b/gyp/common_conditions.gypi
@@ -632,14 +632,6 @@
       },
     ],
 
-    # We can POD-style initialization of static mutexes to avoid generating
-    # static initializers if we're using a pthread-compatible thread interface.
-    [ 'skia_os != "win"', {
-      'defines': [
-        'SK_USE_POSIX_THREADS',
-      ],
-    }],
-
     [ 'skia_moz2d', {
       'defines': [
         # add flags here (e.g. SK_SUPPORT_LEGACY_...) needed by moz2d