update Android auto-detection.

Clang defines __ANDROID__

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2278483004

No public API changes.
TBR=reed@google.com

Review-Url: https://codereview.chromium.org/2278483004
diff --git a/tools/fiddle/fiddle_main.cpp b/tools/fiddle/fiddle_main.cpp
index 49ce50b..bf6a8c2 100644
--- a/tools/fiddle/fiddle_main.cpp
+++ b/tools/fiddle/fiddle_main.cpp
@@ -64,7 +64,7 @@
     return img ? img->encode() : nullptr;
 }
 
-#if defined(__linux)
+#if defined(__linux) && !defined(__ANDROID__)
     #include <GL/osmesa.h>
     static sk_sp<GrContext> create_grcontext() {
         // We just leak the OSMesaContext... the process will die soon anyway.