Rename _LIBCPP_DEBUG2 to _LIBCPP_DEBUG.

llvm-svn: 189140
diff --git a/libcxx/test/strings/basic.string/string.access/db_cfront.pass.cpp b/libcxx/test/strings/basic.string/string.access/db_cfront.pass.cpp
index 55e90e3..d36885e 100644
--- a/libcxx/test/strings/basic.string/string.access/db_cfront.pass.cpp
+++ b/libcxx/test/strings/basic.string/string.access/db_cfront.pass.cpp
@@ -11,7 +11,7 @@
 
 // Call front() on empty const container.
 
-#if _LIBCPP_DEBUG2 >= 1
+#if _LIBCPP_DEBUG >= 1
 
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))