Fix some of the portability issues in lest_expect_abort

[musicinmybrain]

Unconditionally include cstdio for fflush and friends, and cstdlib for abort. When _WIN32 is not defined, include unistd.h instead of io.h for dup and dup2.

This fixes some of the portability issues in lest_expect_abort contrib library, and I guess we can consider that it fixes #39, but it does not entirely fix building lest_expect_abort:

In file included from /home/ben/src/forks/lest/contrib/lest_expect_abort/test/lest_expect_abort.t.cpp:9:
/home/ben/src/forks/lest/contrib/../contrib/lest_expect_abort/lest_expect_abort_cpp03.hpp:85:62: error: expected initializer before ‘abort’
   85 | #  define lest_ABORT_SIGNATURE()  lest_NORETURN void __cdecl abort()
      |                                                              ^~~~~
/home/ben/src/forks/lest/contrib/../contrib/lest_expect_abort/lest_expect_abort_cpp03.hpp:167:1: note: in expansion of macro ‘lest_ABORT_SIGNATURE’
  167 | lest_ABORT_SIGNATURE()
      | ^~~~~~~~~~~~~~~~~~~~
gmake[2]: *** [contrib/lest_expect_abort/test/CMakeFiles/contrib-abort-lest_expect_abort.t_cpp03.dir/build.make:79: contrib/lest_expect_abort/test/CMakeFiles/contrib-abort-lest_expect_abort.t_cpp03.dir/lest_expect_abort.t.cpp.o] Error 1
gmake[2]: Leaving directory '/home/ben/src/forks/lest/build'
gmake[1]: *** [CMakeFiles/Makefile2:601: contrib/lest_expect_abort/test/CMakeFiles/contrib-abort-lest_expect_abort.t_cpp03.dir/all] Error 2
gmake[1]: *** Waiting for unfinished jobs....
In file included from /home/ben/src/forks/lest/contrib/lest_expect_abort/example/00_basic.cpp:2:
/home/ben/src/forks/lest/contrib/../contrib/lest_expect_abort/lest_expect_abort.hpp:87:62: error: expected initializer before ‘abort’
   87 | #  define lest_ABORT_SIGNATURE()  lest_NORETURN void __cdecl abort()
      |                                                              ^~~~~
/home/ben/src/forks/lest/contrib/../contrib/lest_expect_abort/lest_expect_abort.hpp:160:1: note: in expansion of macro ‘lest_ABORT_SIGNATURE’
  160 | lest_ABORT_SIGNATURE()
      | ^~~~~~~~~~~~~~~~~~~~
In file included from /home/ben/src/forks/lest/contrib/lest_expect_abort/example/01_specification.cpp:7:
/home/ben/src/forks/lest/contrib/../contrib/lest_expect_abort/lest_expect_abort.hpp:87:62: error: expected initializer before ‘abort’
   87 | #  define lest_ABORT_SIGNATURE()  lest_NORETURN void __cdecl abort()
      |                                                              ^~~~~
/home/ben/src/forks/lest/contrib/../contrib/lest_expect_abort/lest_expect_abort.hpp:160:1: note: in expansion of macro ‘lest_ABORT_SIGNATURE’
  160 | lest_ABORT_SIGNATURE()
      | ^~~~~~~~~~~~~~~~~~~~
In file included from /home/ben/src/forks/lest/contrib/lest_expect_abort/test/lest_expect_abort.t.cpp:7:
/home/ben/src/forks/lest/contrib/../contrib/lest_expect_abort/lest_expect_abort.hpp:87:62: error: expected initializer before ‘abort’
   87 | #  define lest_ABORT_SIGNATURE()  lest_NORETURN void __cdecl abort()
      |                                                              ^~~~~
/home/ben/src/forks/lest/contrib/../contrib/lest_expect_abort/lest_expect_abort.hpp:160:1: note: in expansion of macro ‘lest_ABORT_SIGNATURE’
  160 | lest_ABORT_SIGNATURE()
      | ^~~~~~~~~~~~~~~~~~~~

Here it looks like the design of lest_expect_abort expects to have the exact signature of abort, and it‘s attempting to satisfy that requirement with some preprocessor conditionals that are both dated and Windows-specific:

lest/contrib/lest_expect_abort/lest_expect_abort.hpp

Lines 75 to 87 in 778597f

	#ifndef lest_ABORT_SIGNATURE
	# if lest_COMPILER_MSVC_VERSION
	# define lest_NORETURN __declspec(noreturn)
	# define lest_ABORT_SIGNATURE() /*_[A]CRTIMP*/ lest_NORETURN void __cdecl abort(void)
	# else
	# define lest_NORETURN [[noreturn]]
	# define lest_ABORT_SIGNATURE() lest_NORETURN void __cdecl abort()
	# endif
	#else
	# ifndef lest_NORETURN
	# define lest_NORETURN
	# endif
	#endif

Well, that’s probably why this is in contrib and not in the main library. Still, this PR should be a step in the right direction for anyone who might be trying to make it work. This is probably the last PR I’ll submit related to the contrib libraries.

[martinmoene]

Thank you for you efforts!

Contents of contrib are the result of several learning attempts which were 'not entirely' convincing, and the products of which I did not want to throw away at the time.