Update to latest LLVM code (#88)

* Update to latest LLVM code.

* Add LLVM's raw_ostream.

* MathExtras.h: Include cmath for log2.

wpiutil/include/llvm/WindowsError.h

@@ -0,0 +1,19 @@
+//===-- WindowsError.h - Support for mapping windows errors to posix-------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_WINDOWSERROR_H
+#define LLVM_SUPPORT_WINDOWSERROR_H
+
+#include <system_error>
+
+namespace llvm {
+std::error_code mapWindowsError(unsigned EV);
+}
+
+#endif