Move atomic_support.h and config_elast.h into src/include

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245354 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/mutex.cpp b/src/mutex.cpp
index 5f8ba0a..127e67a 100644
--- a/src/mutex.cpp
+++ b/src/mutex.cpp
@@ -12,7 +12,7 @@
 #include "limits"
 #include "system_error"
 #include "cassert"
-#include "support/atomic_support.h"
+#include "include/atomic_support.h"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 #ifndef _LIBCPP_HAS_NO_THREADS