Clean up some code in Program.

NFC here, this just raises some platform specific ifdef hackery
out of a class and creates proper platform-independent typedefs
for the relevant things.  This allows these typedefs to be
reused in other places without having to reinvent this preprocessor
logic.

llvm-svn: 334294
diff --git a/llvm/tools/llvm-xray/xray-graph.h b/llvm/tools/llvm-xray/xray-graph.h
index a43df26..fc7f8bb 100644
--- a/llvm/tools/llvm-xray/xray-graph.h
+++ b/llvm/tools/llvm-xray/xray-graph.h
@@ -80,7 +80,7 @@
   using FunctionStack = SmallVector<FunctionAttr, 4>;
 
   using PerThreadFunctionStackMap =
-      DenseMap<llvm::sys::ProcessInfo::ProcessId, FunctionStack>;
+      DenseMap<llvm::sys::procid_t, FunctionStack>;
 
   class GraphT : public Graph<FunctionStats, CallStats, int32_t> {
   public: