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/lib/Support/Unix/Program.inc b/llvm/lib/Support/Unix/Program.inc
index 03599c4..5344adf 100644
--- a/llvm/lib/Support/Unix/Program.inc
+++ b/llvm/lib/Support/Unix/Program.inc
@@ -237,6 +237,7 @@
      return !MakeErrMsg(ErrMsg, "posix_spawn failed", Err);
 
     PI.Pid = PID;
+    PI.Process = PID;
 
     return true;
   }
@@ -300,6 +301,7 @@
   }
 
   PI.Pid = child;
+  PI.Process = child;
 
   return true;
 }