std-coroutine: include for LLVM-14

since std::experimental::coroutine_traits will be removed in LLVM 15,
but are available in LLVM-14.

Update the check to prevent the warning for LLVM-14, as well..

This is a followup to 0a8eea3

Signed-off-by: Ben Pope <ben@redpanda.com>

include/seastar/core/std-coroutine.hh

@@ -21,8 +21,8 @@
 
 #pragma once
 
-// Clang < 15 only supports the TS
-#if __has_include(<coroutine>) && (!defined(__clang__) || __clang_major__ >= 15)
+// Clang < 14 only supports the TS
+#if __has_include(<coroutine>) && (!defined(__clang__) || __clang_major__ >= 14)
 #include <coroutine>
 #define SEASTAR_INTERNAL_COROUTINE_NAMESPACE std
 #elif __has_include(<experimental/coroutine>)