pid_t on 64-bit Windows

[Bruno Haible]

On 64-bit Windows, pid_t needs to be 64-bit large, i.e. intptr_t or 'long long'
or '__int64'.

This is because the return type of _spawnv* (when invoked with _P_NOWAIT) and
the argument of the _cwait function are 'intptr_t' (see [1][2]: "The return
value from an asynchronous _spawnvp or _wspawnvp (_P_NOWAIT or _P_NOWAITO
specified for mode) is the process handle."

On mingw, this is already the case. But on MSVC (and MSVC/clang), the 'pid_t'
type is nowhere defined. In this case, gnulib defines it through config.h.

[1] 
https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/spawnvp-wspawnvp
[2] https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/cwait


2020-08-23  Bruno Haible  <bruno@clisp.org>

        tests: Don't assume that pid_t fits in an 'int'.
        * tests/test-nonblocking-pipe-main.c (main): Use type 'pid_t' instead
        of 'int'.
        * tests/test-nonblocking-socket-main.c (main): Likewise.

        sys_types: Fix definition of pid_t on 64-bit MSVC.
        * m4/pid_t.m4: New file.
        * modules/sys_types (Files): Add it.
        * modules/dirent (Files): Likewise.
        * modules/fcntl-h (Files): Likewise.
        * modules/sched (Files): Likewise.
        * modules/signal-h (Files): Likewise.
        * modules/spawn (Files): Likewise.
        * modules/sys_stat (Files): Likewise.
        * modules/sys_wait (Files): Likewise.
        * modules/termios (Files): Likewise.
        * modules/unistd (Files): Likewise.

0001-sys_types-Fix-definition-of-pid_t-on-64-bit-MSVC.patch
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0002-tests-Don-t-assume-that-pid_t-fits-in-an-int.patch
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