jyasskin@enki:~/opensource/llvm/oprof/dbg$ cat test_config.cc 
#include "llvm/Module.h"

int main() {
}

jyasskin@enki:~/opensource/llvm/oprof/dbg$ ./Debug/bin/llvm-config --cxxflags
-I/usr/local/google/jyasskin/llvm/oprof/dbg/../src/include  -D_DEBUG  -D_GNU_SOURCE -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -g -fPIC  -Woverloaded-virtual

jyasskin@enki:~/opensource/llvm/oprof/dbg$ g++ -c test_config.cc `./Debug/bin/llvm-config --cxxflags` 2>&1|head -20
In file included from /usr/local/google/jyasskin/llvm/oprof/dbg/../src/include/llvm/Value.h:18,
                 from /usr/local/google/jyasskin/llvm/oprof/dbg/../src/include/llvm/User.h:22,
                 from /usr/local/google/jyasskin/llvm/oprof/dbg/../src/include/llvm/Constant.h:17,
                 from /usr/local/google/jyasskin/llvm/oprof/dbg/../src/include/llvm/GlobalValue.h:21,
                 from /usr/local/google/jyasskin/llvm/oprof/dbg/../src/include/llvm/Function.h:21,
                 from /usr/local/google/jyasskin/llvm/oprof/dbg/../src/include/llvm/Module.h:18,
                 from test_config.cc:1:
/usr/local/google/jyasskin/llvm/oprof/dbg/../src/include/llvm/Use.h:29:31: error: llvm/ADT/iterator.h: No such file or directory
...
jyasskin@enki:~/opensource/llvm/oprof/dbg$ ls include/llvm/ADT/iterator.h 
include/llvm/ADT/iterator.h



If llvm-config --cxxflags included "-I/usr/local/google/jyasskin/llvm/oprof/dbg/include", this would compile successfully.