kNumWindows is only used in GPU builds

TBR=csmartdalton@google.com

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2305923004

CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-Clang-GCE-CPU-AVX2-x86_64-Debug-MSAN-Trybot

Committed: https://skia.googlesource.com/skia/+/af92a7f85a5fc774838910444a9f2cddc3e43a2c
Review-Url: https://codereview.chromium.org/2305923004
diff --git a/gm/windowrectangles.cpp b/gm/windowrectangles.cpp
index b4ce7c2..7917bc4 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 @@
 
 #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