Revert "Update aosp/master libcxx rebase to r263688"

The world is burning.

This reverts commit c004fd909c, reversing
changes made to 1418e4163d.

include/cfloat

@@ -67,4 +67,12 @@ Macros:
 #pragma GCC system_header
 #endif
 
+#ifndef FLT_EVAL_METHOD
+#define FLT_EVAL_METHOD __FLT_EVAL_METHOD__
+#endif
+
+#ifndef DECIMAL_DIG
+#define DECIMAL_DIG __DECIMAL_DIG__
+#endif
+
 #endif  // _LIBCPP_CFLOAT