add clang variable for other apps to use

R=dhrosa@google.com
BUG=libyuv:539

Review URL: https://codereview.chromium.org/1557923005 .

README.chromium

 Name: libyuv
 URL: http://code.google.com/p/libyuv/
-Version: 1561
+Version: 1562
 License: BSD
 License File: LICENSE
 

include/libyuv/version.h

@@ -11,6 +11,6 @@
 #ifndef INCLUDE_LIBYUV_VERSION_H_  // NOLINT
 #define INCLUDE_LIBYUV_VERSION_H_
 
-#define LIBYUV_VERSION 1561
+#define LIBYUV_VERSION 1562
 
 #endif  // INCLUDE_LIBYUV_VERSION_H_  NOLINT

libyuv.gyp

@@ -34,6 +34,8 @@
     'libyuv_disable_jpeg%': 0,
     # 'chromium_code' treats libyuv as internal and increases warning level.
     'chromium_code': 1,
+    # clang compiler default variable usable by other apps that include libyuv.
+    'clang%': 0,
     # Link-Time Optimizations.
     'use_lto%': 0,
     'build_neon': 0,