Attempt to fix "Unbundled" build

src/IO/readDecimalText.h

 #pragma once
 
+#include <limits>
 #include <IO/ReadHelpers.h>
 #include <Common/intExp.h>
 
 
+/// This is only needed for non-official, "unbundled" build.
+/// https://stackoverflow.com/questions/41198673/uint128-t-not-working-with-clang-and-libstdc
+#if !defined(_LIBCPP_LIMITS) && !defined(__GLIBCXX_BITSIZE_INT_N_0) && defined(__SIZEOF_INT128__)
+namespace std
+{
+    template <>
+    struct numeric_limits<__int128_t>
+    {
+        static constexpr bool is_specialized = true;
+        static constexpr bool is_signed = true;
+        static constexpr bool is_integer = true;
+        static constexpr int radix = 2;
+        static constexpr int digits = 127;
+        static constexpr int digits10 = 38;
+    };
+}
+#endif
+
+
 namespace DB
 {