Parallelize byte compilation on MS-Windows.

Parallelize byte compilation on MS-Windows.

 lisp/makefile.w32-in (WINS_BASIC1, WINS_BASIC2, WINS_BASIC3)
 (WINS_BASIC4): New variables, subdivide subdirectories into 4
 parts.
 (WINS_BASIC): Define as concatenation of the above.
 (compile): Subdivide into 4 separate and independent jobs that can
 be run in parallel.
 (compile0-CMD, compile0-SH): New targets for compiling
 COMPILE_FIRST files, which are prerequisites for the rest of the
 byte-compilation.
 (compile1-CMD, compile2-CMD, compile3-CMD, compile4-CMD): New
 targets for parallel compilation with cmd.exe.
 (compile1-SH, compile2-SH, compile3-SH, compile4-SH): Ditto for
 compiling under a Unixy shell.