cxxabi: declare abi after __cxxabiv1 namespace

Fixes clang build

Change-Id: Ibf78ee5434387d9b89748431548cd41c6083811d
diff --git a/include/cxxabi.h b/include/cxxabi.h
index 3bd8a58..516e6a8 100644
--- a/include/cxxabi.h
+++ b/include/cxxabi.h
@@ -31,8 +31,6 @@
 
 #include <typeinfo>
 
-namespace abi = __cxxabiv1;
-
 namespace __cxxabiv1
 {
   extern "C" void __cxa_pure_virtual();
@@ -179,5 +177,7 @@
   };
 }
 
+namespace abi = __cxxabiv1;
+
 #endif /* defined(__GABIXX_CXXABI_H__) */