Tidy up file_posix unused variable

CHANGELOG.md

@@ -8,6 +8,7 @@ Version 78:
 * Tidy up FieldsReader doc
 * Add Boost.Locale utf8 benchmark comparison
 * Tidy up dstream for existing Boost versions
+* Tidy up file_posix unused variable
 
 HTTP:
 

include/beast/core/impl/file_posix.ipp

@@ -114,7 +114,9 @@ open(char const* path, file_mode mode, error_code& ec)
         fd_ = -1;
     }
     int f = 0;
+#ifndef __APPLE__
     int advise = 0;
+#endif
     switch(mode)
     {
     default: