Fix setjmp/longjmp-related crashes on Windows

* libguile/Makefile.am: add new header file setjump-win.h
* libguile/continuations.h, libguile/dynstack.c, libguile/dynstack.h,
  libguile/intrinsics.h, libguile/vm.h:
  supply custom `setjmp` macro on Windows

Mingw implements `setjmp (env)` as a macro that expands to

 _setjmp (env, faddr)

where `faddr` is set to the current frame address.

This address is then stored as first element in the jump buffer `env`.
When `longjmp` is called, it tries to unwind the stack up
to the saved address by calling `RtlUnwindEx` from MSVCRT,
which will fail, if the stack frames are interwoven with
JIT-generated code, that violate the Windows x64 calling conventions.

Thus implement the macro ourselves as

_setjmp (env, NULL)

which will toggle a code path in `longjmp` that does no unwinding.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

libguile/dynstack.c

@@ -25,7 +25,12 @@
 #endif
 
 #include <assert.h>
+
+#ifndef _WIN64
 #include <setjmp.h>
+#else
+#include "setjump-win.h"
+#endif
 
 #include "control.h"
 #include "eval.h"