Fix usage of SK_BUILD_* defines.
Since we just 'define' them, but not attribute anything to them, like
'1' for example, cpp expands it to nothing and that breaks the "#if"
clauses.
To fix that, uses "#if defined(...)" which will correctly check if your
macro name was defined or not.
BUG=skia:2850
TEST=make most
R=robertphillips@google.com
Review URL: https://codereview.chromium.org/628763005
diff --git a/tools/skpdiff/SkCLImageDiffer.h b/tools/skpdiff/SkCLImageDiffer.h
index 6e9c2dc..56eccfb 100644
--- a/tools/skpdiff/SkCLImageDiffer.h
+++ b/tools/skpdiff/SkCLImageDiffer.h
@@ -8,7 +8,7 @@
#ifndef SkCLImageDiffer_DEFINED
#define SkCLImageDiffer_DEFINED
-#if SK_BUILD_FOR_MAC
+#if defined(SK_BUILD_FOR_MAC)
# include <OpenCL/cl.h>
#else
# include <CL/cl.h>