Clang fail to find C++ header on non-x86 platform

Hi all,

  Clang seems to have issues while searching for C++ header on non-x86
platforms. One example is test case PCH/cxx-typeid.cpp, clang can't find
header typeinfo on ARM, and PowerPC also has the same problem [1]. At
first, it complains header "typeinfo" can't be found, so I add path
"/usr/include/c++/4.6/". Then it complains header "bits/c++config.h"
can't be found. I add "/usr/include/c++/4.6/arm-linux-gnueabihf"
for it. The final RUN line becomes,

  // RUN: %clang -v -I /usr/include/c++/4.6/ -I /usr/include/c++/4.6/arm-linux-gnueabihf -include %S/cxx-typeid.h -fsyntax-only -Xclang -verify %s

Interesting, this time clang complains it can't find header
"typeinfo". I check this with "-v", and it shows,