win64: make signal handlers work somewhat

we can register a top-level exception filter which does
nothing else than call into _XcptFilter (provided by
the default C runtime environment) and signal handlers
for the few POSIX signals that Windows can handle start
working (that includes e.g. SEGV).

win32/lib/crt1.c

@@ -4,6 +4,7 @@
 // _UNICODE for tchar.h, UNICODE for API
 #include <tchar.h>
 
+#include <windows.h>
 #include <stdio.h>
 #include <stdlib.h>
 
@@ -37,9 +38,19 @@ extern int _tmain(int argc, _TCHAR * argv[], _TCHAR * env[]);
 /* Allow command-line globbing with "int _dowildcard = 1;" in the user source */
 int _dowildcard;
 
+#ifdef __x86_64__
+static LONG WINAPI catch_sig(EXCEPTION_POINTERS *ex)
+{
+  return _XcptFilter(ex->ExceptionRecord->ExceptionCode, ex);
+}
+#endif
+
 void _tstart(void)
 {
     __TRY__
+#ifdef __x86_64__
+     SetUnhandledExceptionFilter(catch_sig);
+#endif
     _startupinfo start_info = {0};
 
     // Sets the current application type

win32/lib/wincrt1.c

@@ -26,6 +26,13 @@ int APIENTRY wWinMain(HINSTANCE, HINSTANCE, LPWSTR, int);
 typedef struct { int newmode; } _startupinfo;
 int __cdecl __tgetmainargs(int *pargc, _TCHAR ***pargv, _TCHAR ***penv, int globb, _startupinfo*);
 
+#ifdef __x86_64__
+static LONG WINAPI catch_sig(EXCEPTION_POINTERS *ex)
+{
+  return _XcptFilter(ex->ExceptionRecord->ExceptionCode, ex);
+}
+#endif
+
 static int go_winmain(TCHAR *arg1)
 {
     STARTUPINFO si;
@@ -54,6 +61,9 @@ static int go_winmain(TCHAR *arg1)
 int _twinstart(void)
 {
     __TRY__
+#ifdef __x86_64__
+     SetUnhandledExceptionFilter(catch_sig);
+#endif
     _startupinfo start_info_con = {0};
     __set_app_type(__GUI_APP);
     __tgetmainargs(&__argc, &__targv, &_tenviron, 0, &start_info_con);