Handle "-" in tryCreateFile.

Otherwise we would fail with -M if the we didn't have write
permissions to the current directory.

llvm-svn: 317740
diff --git a/lld/ELF/Filesystem.cpp b/lld/ELF/Filesystem.cpp
index 1aa3453..a7c25c9 100644
--- a/lld/ELF/Filesystem.cpp
+++ b/lld/ELF/Filesystem.cpp
@@ -80,5 +80,7 @@
 std::error_code elf::tryCreateFile(StringRef Path) {
   if (Path.empty())
     return std::error_code();
+  if (Path == "-")
+    return std::error_code();
   return errorToErrorCode(FileOutputBuffer::create(Path, 1).takeError());
 }