Few fixes for Windows/Visual Studio builds

Hi,

The latest GIT master had some items that needed updating for Windows/Visual Studio builds to work, namely:

• We are trying to go from GThread * to unsigned long in gtlsbackend-openssl.c, which only works ok on 32-bit builds, since sizeof(unsigned long) is always 4 for all Visual Studio (32/64-bit) builds. We can use size_t instead for this to fix this.

• In tls/base/gtlslog.h, we are using GCC-style varargs here, which is not supported on non-GCC-style compilers. So, we use ISO C-style varargs on non-GCC instead.

With blessings, thank you!