fies the current platform.

    This is used mainly to distinguish platform-specific build directories and
    platform-specific built distributions.  Typically includes the OS name and
    version and the architecture (as supplied by 'os.uname()'), although the
    exact information included depends on the OS; on Linux, the kernel version
    isn't particularly important.

    Examples of returned values:
       linux-i586
       linux-alpha (?)
       solaris-2.6-sun4u

    Windows will return one of:
       win-amd64 (64-bit Windows on AMD64 (aka x86_64, Intel64, EM64T, etc)
       win-arm64 (64-bit Windows on ARM64 (aka AArch64)
       win32 (all others - specifically, sys.platform is returned)

    For other non-POSIX platforms, currently just returns 'sys.platform'.

    r