Build libunwind, enable exceptions in libcxxabi and libcxx

This requires manually enabling sjlj exceptions, since libunwind
doesn't support the other exception handling mechanisms on windows
(yet).

Don't enable exceptions on aarch64 yet, since no exception handling
mechanism is implemented for windows on aarch64 yet.

hello-exception.cpp

@@ -0,0 +1,49 @@
+#include <iostream>
+#include <stdio.h>
+
+class Hello {
+public:
+	Hello() {
+		printf("Hello ctor\n");
+	}
+	~Hello() {
+		printf("Hello dtor\n");
+	}
+};
+
+Hello global_h;
+
+class RecurseClass {
+public:
+	RecurseClass(int v) : val(v) {
+		printf("ctor %d\n", val);
+	}
+	~RecurseClass() {
+		printf("dtor %d\n", val);
+	}
+private:
+	int val;
+};
+
+void recurse(int val) {
+	RecurseClass obj(val);
+	if (val == 0) {
+		throw std::exception();
+	}
+	if (val == 5) {
+		try {
+			recurse(val - 1);
+		} catch (std::exception& e) {
+			printf("caught exception at %d\n", val);
+		}
+	} else {
+		recurse(val - 1);
+	}
+	printf("finishing function recurse %d\n", val);
+}
+
+int main(int argc, char* argv[]) {
+	std::cout<<"Hello world C++"<<std::endl;
+	recurse(10);
+	return 0;
+}