kNumWindows is only used in GPU builds

gm/windowrectangles.cpp

Index: gm/windowrectangles.cpp
diff --git a/gm/windowrectangles.cpp b/gm/windowrectangles.cpp
index 4b7519962f69d7ea4513f5dfd8c1ffe708d2b30d..96c4ea6e4899fea0d0fa808d55da9732950b35b8 100644
--- a/gm/windowrectangles.cpp
+++ b/gm/windowrectangles.cpp
@@ -23,7 +23,6 @@
 constexpr static SkIRect kDeviceRect = {0, 0, 600, 600};
 constexpr static SkIRect kLayerRect = {25, 25, 575, 575};
 constexpr static SkIRect kCoverRect = {50, 50, 550, 550};
-constexpr static int kNumWindows = 8;
 
 namespace skiagm {
 
@@ -107,6 +106,8 @@ DEF_GM( return new WindowRectanglesGM(); )
 
 #if SK_SUPPORT_GPU
 
+constexpr static int kNumWindows = 8;
+
 /**
  * Visualizes the mask (alpha or stencil) for a clip with several window rectangles. The purpose of
  * this test is to verify that window rectangles are being used during clip mask generation, and to