lib9/main.c: don't show the crash dialog on windows

Fixes #3202. (Or rather, work around issue 3202)

R=alex.brainman, rsc
CC=golang-dev
https://golang.org/cl/7202053

src/lib9/main.c

@@ -27,11 +27,28 @@ THE SOFTWARE.
 #define NOPLAN9DEFINES
 #include <libc.h>
 
+#ifdef WIN32
+#include <windows.h>
+
+static void crashhandler() {
+	fprint(2, "%s: internal fatal error.\n", argv0);
+	exit(1);
+}
+#endif
+
 extern void p9main(int, char**);
 
 int
 main(int argc, char **argv)
 {
+#ifdef WIN32
+	signal(SIGSEGV, crashhandler);
+	signal(SIGBUS, crashhandler);
+	// don't display the crash dialog
+	DWORD mode = SetErrorMode(SEM_NOGPFAULTERRORBOX);
+	SetErrorMode(mode | SEM_FAILCRITICALERRORS | SEM_NOGPFAULTERRORBOX | SEM_NOOPENFILEERRORBOX);
+	argv0 = argv[0];
+#endif
 	p9main(argc, argv);
 	exits("main");
 	return 99;