[PATCH] Fix path concatenation in HeaderSearch

[Yaron Keren]

// REQUIRES: system-windows

run on Windows 7 results in

UNSUPPORTED: LLVM :: Other/path-seperator.c (1 of 1)

what feature work with requires? In other test I have seen REQUIRES: asserts, zlib, nozlib but no OS example.

http://reviews.llvm.org/D3686