Support --output-sync on MS-Windows.

Support --output-sync on MS-Windows.

 w32/compat/posixfcn.c: New file, with emulations of Posix
 functions and Posix functionality for MS-Windows.
 w32/subproc/sub_proc.c: Include io.h.
 (process_noinherit): New function, forces a file descriptor to not
 be inherited by child processes.
 (process_easy): Accept two additional arguments, and use them to
 set up the standard output and standard error handles of the child
 process.
 w32/include/sub_proc.h (process_easy): Adjust prototype.
 (process_noinherit): Add prototype.

 read.c [WINDOWS32]: Include windows.h and sub_proc.h.
 makeint.h (LOCALEDIR) [WINDOWS32}: Define to NULL if not
 defined.  This is needed because the MS-Windows build doesn't have
 a canonical place for LOCALEDIR.
 (WIN32_LEAN_AND_MEAN) [WINDOWS32]: Define, to avoid getting from
 windows.h header too much stuff that could conflict with the code.
 main.c <sync_mutex>: New static variable.
 <switches>: Add support for "--sync-mutex" switch.
 (decode_output_sync_flags): Decode the --sync-mutex= switch.
 (prepare_mutex_handle_string) [WINDOWS32]: New function.
 (main): Add "output-sync" to .FEATURES.
 job.h (CLOSE_ON_EXEC) [WINDOWS32]: Define to call
 process_noinherit.
 (F_GETFD, F_SETLKW, F_WRLCK, F_UNLCK, struct flock) [WINDOWS32]:
 New macros.
 (RECORD_SYNC_MUTEX): New macro, a no-op for Posix platforms.
 (sync_handle_t): New typedef.
 job.c <sync_handle>: Change type to sync_handle_t.
 (FD_NOT_EMPTY): Seek to the file's end.  Suggested by Frank
 Heckenbach <f.heckenbach@fh-soft.de>.
 (pump_from_tmp_fd) [WINDOWS32]: Switch to_fd to binary mode for
 the duration of this function, and then change back before
 returning.
 (start_job_command) [WINDOWS32]: Support output_sync mode on
 MS-Windows.  Use a system-wide mutex instead of locking
 stdout/stderr.  Call process_easy with two additional arguments:
 child->outfd and child->errfd.
 (exec_command) [WINDOWS32]: Pass two additional arguments, both
 -1, to process_easy, to adjust for the changed function signature.
 function.c (windows32_openpipe) [WINDOWS32]: This function now
 returns an int, which is -1 if it fails and zero otherwise.  It
 also calls 'error' instead of 'fatal', to avoid exiting
 prematurely.
 (func_shell_base) [WINDOWS32]: Call perror_with_name if
 windows32_openpipe fails, now that it always returns.  This avoids
 a compiler warning that error_prefix is not used in the MS-Windows
 build.
 config.h.W32.template (OUTPUT_SYNC): Define.
 build_w32.bat: Add w32/compat/posixfcn.c to compilation and
 linking commands.

 From Frank Heckenbach <f.heckenbach@fh-soft.de>:
 job.c (sync_output): Don't discard the output if
 acquire_semaphore fails; instead, dump the output unsynchronized.