test/Index/preamble_macro_template.cpp: Tweak for win32.

Using the file immediately after "> file 2>&1" causes weird behavior on win32.
For example, "foo > %t 2>&1; FileCheck --input-file=%t"

Use "foo 2>&1 | tee %t" instead.

Note, mixing stdout and stderr to the same handle might cause unexpected behavior, due to buffering.

llvm-svn: 171009