Provide the ThrowErrno utility.
Patch contributed by Morten Ofstad


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17827 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/System/Win32/Win32.h b/lib/System/Win32/Win32.h
index fb2c7e9..ab6b3c2 100644
--- a/lib/System/Win32/Win32.h
+++ b/lib/System/Win32/Win32.h
@@ -31,3 +31,6 @@
   throw s;
 }
 
+inline void ThrowErrno(const std::string& prefix) {
+    ThrowError(prefix + ": " + strerror(errno));
+}