Improve basic block ordering for some loops.

Currently the compiler rotates most loops to minimize branching costs,
but for some loops this actually has the opposite effect (i.e., larger
and slower code being generated), namely for those that already have the
termination test at the end.

So, inhibit loop rotation if such a loop is detected. The decision is
based upon whether the loop's back edge starts with a conditional branch
(don't rotate) or an unconditional branch (do rotate). This heuristic is
correct in simple cases but may err, e.g. if a loop has multiple back
edges. As we didn't try before and don't try now to analyse complex
loops to aid the decision whether to rotate or not, or even how far,
hopefully any differences introduced here will cancel on average with
respect to their impact on performance and code size.

(Loops consisting of only one basic block -- which necessarily have the
termination test at the end -- were (obviously) treated correctly
already. But even small loops can easily consist of multiple blocks, for
example if the loop body contains code from inlining a function call.)
Windows: Use overlapped I/O, CreateFile

Overlapped I/O is win32's asynchronous I/O mechanism, which allows
us to start an I/O operation and explicitly wait for it to finish at
a time of our choosing, such that we can simultaneously await other
events instead of blocking unconditionally.

  - Support for overlapped I/O is a per-HANDLE flag specified at
    file opening time, necessitating a switch to win32's CreateFile
    and away from the CRT's _open.

  - Wrap win32 file operations in POSIX-compatible functions, so
    that UNIX-OPEN, UNIX-READ, UNIX-WRITE, UNIX-CLOSE continue to
    work as before.  Under the hood, these now call our Lisp or C
    functions instead of versions from CRT.

  - For now, these functions still return and expect what passes as
    file descriptors in CRT.

  - INTERRUPT-THREAD is now capable of performing the interruption
    in a target thread blocked in socket I/O, indicated using an
    errno of "EINTR".  Minor changes in FD streams to retry the I/O
    operation explicitly in that case.

Does not yet include changes for console I/O, and instead still
falls back to _read and _write in that case.  Also not yet included
is interruptible non-overlapped I/O, e.g. for unnamed pipes.

Thanks to Anton Kovalenko.
sb-bsd-sockets: Add a test for interruptible I/O

Test TCP sockets even without :internet-available, albeit only on
threaded builds.  Check that INTERRUPT-THREAD works in a timely
fashion on threads currently blocked in I/O on a socket.
Update NEWS, make-config.sh
src/runtime/sparc-arch.c: Use si_addr in arch_get_bad_addr().

  * Since the sparc port was first merged, arch_get_bad_addr() has
only worked when the program counter is within read-only or the
current dynamic space.

  * This is fragile simply because of the existance of static
space and PURIFY.  It is WORSE when you add GENCGC to the mix (to
the point where SunOS with GENCGC doesn't even call
arch_get_bad_addr() anymore).

  * The existing implementation looks like it predates the switch
to sigaction(2) style signal handlers.  SBCL uses si_addr on all
other backends save Alpha (long undermaintained) and HPPA (even
longer undermaintained).  Clearly, this approach works on SunOS.
From testing, it works on at least linux-2.6.32.  We might as well
run with it, since we need it for GENCGC anyway, and we can easily
concoct a test case that would cause a failure using CHENEYGC.

  * So, implementation patterned on any of the other backends, but
leaving the old code in place, conditional-compiled out, as a bit
of a historical note / warning to future historians.
GENCGC on SPARC/Linux

  * Tweak make-config.sh to automatically select GENCGC, and to
update the fallback message for those poor bsd-using folks.

  * Copied the gencgc memory map from the SunOS version to use for
Linux (the cheneygc maps were identical, we may as well keep the
parallelism).

  * Also tweaked the linker flags to match.  Not because it was
required to build, but because I don't know why they were changed
for SunOS, and in the absence of such knowledge I'd rather keep
things more or less parallel.
Disable an SB-INTROSPECT test on GENCGC SPARC.

  * Test ALLOCATION-INFORMATION.4 is known to be flaky at best on
GENCGC PPC, and has been observed to fail on GENCGC SPARC.  Since
it's been marked :FAILS-ON for GENCGC PPC, mark it as failing for
GENCGC SPARC as well.
.gitignore: Add src/runtime/sparc-funcdef.h

  * Just another auto-generated file for a rarely-maintained
target.