[HIP] Use nul instead of /dev/null when running on windows

When clang is running on windows, /dev/null is not available. Use nul as empty input file instead.

Differential Revision: https://reviews.llvm.org/D56225

llvm-svn: 350885
diff --git a/clang/lib/Driver/ToolChains/HIP.cpp b/clang/lib/Driver/ToolChains/HIP.cpp
index b44aadd..868765c 100644
--- a/clang/lib/Driver/ToolChains/HIP.cpp
+++ b/clang/lib/Driver/ToolChains/HIP.cpp
@@ -24,6 +24,12 @@
 using namespace clang;
 using namespace llvm::opt;
 
+#if _WIN32 || _WIN64
+#define NULL_FILE "nul"
+#else
+#define NULL_FILE "/dev/null"
+#endif
+
 namespace {
 
 static void addBCLib(Compilation &C, const ArgList &Args,
@@ -197,7 +203,7 @@
   // ToDo: Remove the dummy host binary entry which is required by
   // clang-offload-bundler.
   std::string BundlerTargetArg = "-targets=host-x86_64-unknown-linux";
-  std::string BundlerInputArg = "-inputs=/dev/null";
+  std::string BundlerInputArg = "-inputs=" NULL_FILE;
 
   for (const auto &II : Inputs) {
     const auto* A = II.getAction();