Replace all uses of PathV1::isAbsolute with PathV2::is_{absolute,relative}.

llvm-svn: 122087
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index a4ba496..724ebdf 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -1703,7 +1703,7 @@
   if (!RelocatablePCH)
     return;
 
-  if (Filename.empty() || llvm::sys::Path(Filename).isAbsolute())
+  if (Filename.empty() || llvm::sys::path::is_absolute(Filename))
     return;
 
   if (isysroot == 0) {