Clang cant find normal includes from c++, it misses the libstdc++ include paths:

pandora:~/tmp> clang++ -v -o s sort.cc
clang version 6.0.0 (tags/RELEASE_600/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
 "/usr/bin/clang-6.0" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name sort.cc -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -v -resource-dir /usr/lib64/clang/6.0.0 -internal-isystem /usr/local/include -internal-isystem /usr/lib64/clang/6.0.0/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir /home/magallon/tmp -ferror-limit 19 -fmessage-length 80 -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o /tmp/magallon/sort-72edd4.o -x c++ sort.cc
clang -cc1 version 6.0.0 based upon LLVM 6.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib64/clang/6.0.0/include
 /usr/include
End of search list.
sort.cc:2:10: fatal error: 'string' file not found
#include <string>
         ^~~~~~~~
1 error generated.