Add our system name to checks here and there

When the check doesn't concern kernel,
but userland stuff (notably, libc),
we want to match the same checks that match Linux.
Make sure the definitions
are not simply duplicated from Linux' because that will
eventualy result in
out-of-sync definitions that break for us.

Example of triplet check:linux*-gnu | gnu* | k*bsd*-gnu)
Example of uname check: Linux|GNU|GNU/*)
Example of C macro check:
defined(__linux__) || defined(__GNU__) || defined(__GLIBC__)

[note: GNU/Hurd defines __GNU__,
and GNU/k*BSD define __GLIBC__ as hardcoded macro]
Example of makefile check:
ifneq (, $(filter Linux GNU GNU_%, $(shell uname -s)))

[note1: findstring matches subwords, use filter instead]

[note2: list must be the first parameter, otherwise matching fails]
				[note3: "%" is make's wildcard]

When the check concerns kernel, we obviously want to match with
 FreeBSD's
Example of triplet check: Freebsd* | kfreebsd*-gnu)
Example of uname check:	  *FreeBSD)
Example of C macro check: defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
			  [note: see below for more details on this one]
debian/control files
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