Merge the [pgoyette-compat] branch

Define compat modules (but without dependencies yet).

Make the emulations, exec formats, coredump, NFS, and the NFS server
into modules. By and large this commit:

- shuffles header files and ifdefs
- splits code out where necessary to be modular
- adds

Make the emulations, exec formats, coredump, NFS, and the NFS server
into modules. By and large this commit:

- shuffles header files and ifdefs
- splits code out where necessary to be modular
- adds module glue for each of the components
- adds/replaces hooks for things that can be installed at runtime

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- Add compat amd64 linux32 statfs support, adapted from PR/35956.
- Move bsd_to_linux_statfs() function to its own file to be shared
between both linux compats.

ok by manu.

Jumbo COMPAT_LINUX/COMPAT_LINUX32 bugfix, with the help of Nicolas Joly
- Fix shmat return value on amd64: it uses no black magic with retval[0]
- Fix integer overflows in sysinfo
- Implement sysinfo

Jumbo COMPAT_LINUX/COMPAT_LINUX32 bugfix, with the help of Nicolas Joly
- Fix shmat return value on amd64: it uses no black magic with retval[0]
- Fix integer overflows in sysinfo
- Implement sysinfo, mmap2, sched_getparam, sched_getscheduler, mremap,
and madvise in COMPAT_LINUX32
- Fix improper types used in setgroups16/getgroups16
- Implement mmap2 for COMPAT_LINUX32
- Ifdef debug messages by DEBUG_LINUX

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- Move the BSD to Linux and Linux to BSD termio/termios conversion functions
to a header where they can be shared between COMPAT_LINUX and COMPAT_LINUX32
- Add termios ioctl emulation to COMPAT_LINUX

- Move the BSD to Linux and Linux to BSD termio/termios conversion functions
to a header where they can be shared between COMPAT_LINUX and COMPAT_LINUX32
- Add termios ioctl emulation to COMPAT_LINUX32
- Add the getcwd system call to COMPAT_LINUX32/amd64

That makes Linux's bash working with COMPAT_LINUX32.

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Add initial (but unfinished) COMPAT_LINUX32 for amd64. This is good enough so
that the i386 license manager part of amd64 version of Fluent works.

While I'm here, add SysV IPC to COMPAT_LINUX/amd64