I can't compile VLC on NetBSD/alpha. If you want to have a full build log and all, please contact me at weel at caltech dot edu (I don't read this forum) and I'll try the build again and get you a log file, but basically this is why it doesn't build:
in include/vlc_threads_funcs.h , the assumption is being made repeatedly that you can cast a pointer to a pthread to an int. Pointers to threads are stored in various variables and return values of type int, which just doesn't fly on an alpha, which is a 64 bit processor. On the alpha, int is 32 bits and a pointer is 64 bits. This is why pointers should be stored in variables that have a pointer type. If it is not clear what the pointer type should be, or you don't want to have to export that type definition to lots of other files, you can just use void*, but not int. ANSI C does not prescribe that your way needs to work, and your approach may or may not break on other 64 bit machines (some of them have 64 bit ints by default; on the alpha, long is defined to be 64 bits.)