Gate disabling nacl code on proper gyp flags, etc.

build/build_config.h

Index: build/build_config.h
diff --git a/build/build_config.h b/build/build_config.h
index c384347bcf17ae1dd519063212f3bcb4823cee0d..6e31a730918e959fb76855fb79f295279061a5f9 100644
--- a/build/build_config.h
+++ b/build/build_config.h
@@ -4,7 +4,7 @@
 
 // This file adds defines about the platform we're currently building on.
 //  Operating System:
-//    OS_WIN / OS_MACOSX / OS_LINUX / OS_POSIX (MACOSX or LINUX)
+//    OS_WIN / OS_MACOSX / OS_LINUX / OS_POSIX (MACOSX or LINUX) / OS_NACL
 //  Compiler:
 //    COMPILER_MSVC / COMPILER_GCC
 //  Processor:
@@ -19,15 +19,16 @@
 #endif
 
 // A set of macros to use for platform detection.
-#if defined(ANDROID)
+#if defined(__native_client__)
+// __native_client__ must be first, so that other OS_ defines are not set.
+#define OS_NACL 1
+#elif defined(ANDROID)
 #define OS_ANDROID 1
 #elif defined(__APPLE__)
 #define OS_MACOSX 1
 #if defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE
 #define OS_IOS 1
 #endif  // defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE
-#elif defined(__native_client__)
-#define OS_NACL 1
 #elif defined(__linux__)
 #define OS_LINUX 1
 // include a system header to pull in features.h for glibc/uclibc macros.