[fuchsia] GN build support for Fuchsia OS and fuchsia_test target

runtime/platform/globals.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef PLATFORM_GLOBALS_H_
 #define PLATFORM_GLOBALS_H_
 
 // __STDC_FORMAT_MACROS has to be defined before including <inttypes.h> to
 // enable platform independent printf format specifiers.
 #ifndef __STDC_FORMAT_MACROS
@@ skipping 95 matching lines @@
 // '#if defined(TARGET_OS_IOS)'. TARGET_OS_IOS is defined to be 0 in
 // XCode >= 7.0. See Issue #24453.
 #define TARGET_OS_IOS 1
 #endif
 
 #elif defined(_WIN32)
 
 // Windows, both 32- and 64-bit, regardless of the check for _WIN32.
 #define TARGET_OS_WINDOWS 1
 
+#elif defined(__Fuchsia__)
+#define TARGET_OS_FUCHSIA
+
 #elif !defined(TARGET_OS_FUCHSIA)
 #error Automatic target os detection failed.
 #endif
 
 
 // Setup product, release or debug build related macros.
 #if defined(PRODUCT) && defined(DEBUG)
 #error Both PRODUCT and DEBUG defined.
 #endif  // defined(PRODUCT) && defined(DEBUG)
 
@@ skipping 565 matching lines @@
 // tag in the ICData and check it when recreating the flow graph in
 // optimizing compiler. Enable it for other modes (product, release) if needed
 // for debugging.
 #if defined(DEBUG)
 #define TAG_IC_DATA
 #endif
 
 }  // namespace dart
 
 #endif  // PLATFORM_GLOBALS_H_