Merge pull request #12844 from ghalliday/issue18377

HPCC-18377 Fix windows exported symbol build error

Reviewed-By: Shamser Ahmed <shamser.ahmed@lexisnexis.co.uk>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>

system/jlib/jlog.hpp

@@ -509,9 +509,9 @@ protected:
     bool                      remoteFlag;
 };
 
-unsigned getPositionOfField(unsigned logfields, unsigned positionoffield);
-unsigned getMessageFieldsFromHeader(const char * line);
-unsigned getMessageFieldsFromHeader(FILE *handle);
+jlib_decl unsigned getPositionOfField(unsigned logfields, unsigned positionoffield);
+jlib_decl unsigned getMessageFieldsFromHeader(const char * line);
+jlib_decl unsigned getMessageFieldsFromHeader(FILE *handle);
 
 // INTERFACES