Support/PathV2: Move current_path from path to fs and fix the Unix implementation.

Unix bug spotted by Dan Gohman.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121090 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/PathV2.cpp b/lib/Support/PathV2.cpp
index 639b323..492903e 100644
--- a/lib/Support/PathV2.cpp
+++ b/lib/Support/PathV2.cpp
@@ -437,7 +437,7 @@
 
   // All of the following conditions will need the current directory.
   SmallString<128> current_dir;
-  if (error_code ec = current_path(current_dir)) return ec;
+  if (error_code ec = fs::current_path(current_dir)) return ec;
 
   // Relative path. Prepend the current directory.
   if (!rootName && !rootDirectory) {