[asan] flatten the asan-rt build slightly

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@145631 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/asan/asan_linux.cc b/lib/asan/asan_linux.cc
index 752300b..ceb722b 100644
--- a/lib/asan/asan_linux.cc
+++ b/lib/asan/asan_linux.cc
@@ -11,6 +11,7 @@
 //
 // Linux-specific details.
 //===----------------------------------------------------------------------===//
+#ifdef __linux__
 
 #include "asan_internal.h"
 
@@ -46,3 +47,5 @@
 }
 
 }  // namespace __asan
+
+#endif  // __linux__