#1537 Lib.c does not respect USE_VICE_THREAD

[Carlo Bramini]

Hello,
when I was building my VICE port for Windows CE/Mobile I got an error because pthread.h is not found, although its support has been disabled when I launched configure script.
This happens into src/lib.c, because pthread.h is included two time.
There is one inclusion on top of the file, which is wrong and it must be removed.
Then, there is a second inclusion of pthread.h, but this is enabled by an #ifdef USE_VICE_THREAD...#endif, so this is correct.
The fix is very simple, I attached a patch to show the correction.

[gpz]

applied in r40599 - thanks!