Missing headers and wrong function names for MSVC.
Add an option to premake configuration for pthreads-w32 location.
Don't specify name of DLL in .def file.
Encode major version explicitly in liblo.def.

Don't specify library name when building from MSVC.  (Depends on project
target.)

The major version is calculated from LO_SO_VERSION, so must be calculated at
autoconf time when generating configure.  The LO_SO_VERSION parts are
therefore independently represented now, instead of parsing the string and
depending on shell-based calculations.