include: fix build with older clang

to fix the FTBFS on clang shipped with xcode 9.1 (based on Clang 4.0).
This fixes ceph client library builds for the OSX target
initally targetted with PR #23034.

refs: #23034

Signed-off-by: Christopher Blum <zeichenanonym@web.de>

diff --git a/src/common/convenience.h b/src/common/convenience.h
index e95fafe849a8fb27516830c1fa6e73f9115950e0..9dc2ed1b422930ef2ce73e5bbbed50ac87afd3ea 100644 (file)
--- a/src/common/convenience.h
+++ b/src/common/convenience.h
@@ -32,7 +32,6 @@
 #ifndef CEPH_COMMON_CONVENIENCE_H
 #define CEPH_COMMON_CONVENIENCE_H
 
-#if __has_include(<optional>)
 namespace ceph {
 
 // Lock Factories
@@ -150,7 +149,6 @@ inline auto with_shared_lock(Mutex&& mutex, Fun&& fun, Args&&... args)
   return std::forward<Fun>(fun)(std::forward<Args>(args)...);
 }
 }
-#endif // __has_include(<optional>)
 
 // Lock Types
 // ----------
@@ -205,7 +203,7 @@ auto maybe_do_or(const boost::optional<T>& t, F&& f, U&& u) ->
     return std::forward<U>(u);
 }
 
-
+#if __has_include(<optional>)
 // Same thing but for std::optional
 
 template<typename T, typename F>
@@ -233,6 +231,8 @@ auto maybe_do_or(const std::optional<T>& t, F&& f, U&& u) ->
   else
     return std::forward<U>(u);
 }
+#endif // __has_include(<optional>)
+
 
 namespace _convenience {
 template<typename... Ts, typename F,  std::size_t... Is>