[cxx-interop] Fix libstdc++ build failure on CentOS 7

CentOS 7 is shipped with an outdated version of libstdc++, which does not include `codecvt` stdlib header.
Let's wrap the `#include` with `#if __has_include`.

Author: egorzhdan

stdlib/public/Cxx/libstdcxx.h

@@ -33,7 +33,6 @@
 #include "array"
 #include "atomic"
 #include "chrono"
-#include "codecvt"
 #include "condition_variable"
 #include "forward_list"
 #include "future"
@@ -51,6 +50,11 @@
 #include "unordered_map"
 #include "unordered_set"
 
+// libstdc++ 4.8.5 bundled with CentOS 7 does not include corecvt.
+#if __has_include("codecvt")
+#include "codecvt"
+#endif
+
 // C++17 and newer:
 
 #if __has_include("any")