Various private imports in Qt modules are not declared with appropriate __declspec(dllimport) statements

In lots of places people have assumed extern is enough to import a symbol from another module. On DLL-based platforms this isn't enough (you need __declspec(dllimport)), and RVCT4 is far stricter about this than RVCT2.2. Fixes are something like:

-extern double qstrtod(const char *s00, char const **se, bool *ok);
+Q_DECL_IMPORT extern double qstrtod(const char *s00, char const **se, bool *ok);

A similar issue exists when exporting a symbol from a module - extern is not enough, it needs to be __declspec(dllexport), in all locations, including references as well as definitions.