Fix host detection for Android

Turns out the right macro to use to detect whether we are
building for an Android device is __ANDROID__.
ANDROID means "build in the Android tree".

Bug: 73283884
Change-Id: I0fe8943e1294d79e6c4d9eef8656d6054309e508
diff --git a/include/perfetto/base/build_config.h b/include/perfetto/base/build_config.h
index b04321d..de4a436 100644
--- a/include/perfetto/base/build_config.h
+++ b/include/perfetto/base/build_config.h
@@ -24,7 +24,7 @@
 #define PERFETTO_BUILDFLAG(flag) \
   (PERFETTO_BUILDFLAG_CAT(PERFETTO_BUILDFLAG_DEFINE_, flag)())
 
-#if defined(ANDROID)
+#if defined(__ANDROID__)
 #define PERFETTO_BUILDFLAG_DEFINE_PERFETTO_OS_ANDROID() 1
 #define PERFETTO_BUILDFLAG_DEFINE_PERFETTO_OS_MACOSX() 0
 #define PERFETTO_BUILDFLAG_DEFINE_PERFETTO_OS_LINUX() 0