Implement backtraces on Windows.

Much !!FUN!! was had

WinBacktrace.h

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+/* Copyright 2014 MultiMC Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <windows.h>
+
+#ifndef SF_STR_LEN
+// The max length of all strings in the StackFrame struct.
+// Because it must be stack allocated, this must be known at compile time.
+// Stuff longer than this will be truncated.
+// Defaults to 4096 (4kB)
+#define SF_STR_LEN 4096
+#endif
+
+// Data structure for holding information about a stack frame.
+// There's some more hackery in here so it can be allocated on the stack.
+struct StackFrame
+{
+	// The address of this stack frame.
+	void* address;
+
+	// The name of the function at this address.
+	char funcName[SF_STR_LEN];
+};
+
+// This function walks through the given CONTEXT structure, extracting a
+// backtrace from it.
+// The backtrace will be put into the array given by the `stack` argument
+// with a maximum length of `size`.
+// This function returns the size of the backtrace retrieved.
+size_t getBacktrace(StackFrame* stack, size_t size, CONTEXT ctx);