Fix ~1000 warnings class/struct mismatch.

Handle this warning in the future as error, this will prevent pushing to main trees.

cmake/os/Windows.cmake

@@ -110,6 +110,10 @@ IF(MSVC)
     ADD_DEFINITIONS(/wd4996)
   ENDIF()
 
+  # Make class/struct definition mismatch an error (overseen too often,
+  # adds tons of new warnings)
+  ADD_DEFINITIONS(/we4099)
+
   IF(CMAKE_SIZEOF_VOID_P MATCHES 8)
     # _WIN64 is defined by the compiler itself. 
     # Yet, we define it here again   to work around a bug with  Intellisense 

sql/sql_lex.h

@@ -998,7 +998,7 @@ extern const LEX_STRING null_lex_str;
 extern const LEX_STRING empty_lex_str;
 
 
-struct Sroutine_hash_entry;
+class Sroutine_hash_entry;
 
 /*
   Class representing list of all tables used by statement and other