clang is using the wrong system include directory

My workstation is RHEL 6.5, which came with gcc 4.4.7 preinstalled. We are doing C++11 work, so we purchased the RedHat Developer's Toolset set of repositories, which includdes G++ 4.8.2. Both versions of G++ are installed on this machine, but 4.8.2 is the version that is invoked when launched from the command line and via a build:

john@hurricane /home/john/repo/phoenix [PHX-29|✚5] $ which g++ /opt/rh/devtoolset-2/root/usr/bin/g++ john@hurricane /home/john/repo/phoenix [PHX-29|✚5] $ g++ --version g++ (GCC) 4.8.2 20140120 (Red Hat 4.8.2-15) Copyright (C) 2013 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 

Note the unusual install location.

I've also built clang from source and installed it. However when I build C++11 projects using clang, clang is picking up the wrong system includes. It's picking up the system headers from gcc 4.4.7, rather than from 4.8.2.

G++ configuration:

john@hurricane /home/john/repo/phoenix [PHX-29|✚5] $ g++ -E -x c++ - -v < /dev/null Using built-in specs. COLLECT_GCC=g++ Target: x86_64-redhat-linux Configured with: ../configure --prefix=/opt/rh/devtoolset-2/root/usr --mandir=/opt/rh/devtoolset-2/root/usr/share/man --infodir=/opt/rh/devtoolset-2/root/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --enable-languages=c,c++,fortran,lto --enable-plugin --with-linker-hash-style=gnu --enable-initfini-array --disable-libgcj --with-isl=/builddir/build/BUILD/gcc-4.8.2-20140120/obj-x86_64-redhat-linux/isl-install --with-cloog=/builddir/build/BUILD/gcc-4.8.2-20140120/obj-x86_64-redhat-linux/cloog-install --with-mpc=/builddir/build/BUILD/gcc-4.8.2-20140120/obj-x86_64-redhat-linux/mpc-install --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux Thread model: posix gcc version 4.8.2 20140120 (Red Hat 4.8.2-15) (GCC) COLLECT_GCC_OPTIONS='-E' '-v' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /opt/rh/devtoolset-2/root/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/cc1plus -E -quiet -v -D_GNU_SOURCE - -mtune=generic -march=x86-64 ignoring nonexistent directory "/opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include-fixed" ignoring nonexistent directory "/opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../x86_64-redhat-linux/include" #include "..." search starts here: #include <...> search starts here: /opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2 /opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/x86_64-redhat-linux /opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/backward /opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/include /usr/local/include /opt/rh/devtoolset-2/root/usr/include /usr/include End of search list. # 1 "<stdin>" # 1 "<command-line>" # 1 "<stdin>" COMPILER_PATH=/opt/rh/devtoolset-2/root/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/:/opt/rh/devtoolset-2/root/usr/libexec/gcc/x86_64-redhat-linux/4.8.2/:/opt/rh/devtoolset-2/root/usr/libexec/gcc/x86_64-redhat-linux/:/opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/:/opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/ LIBRARY_PATH=/opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/:/opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/opt/rh/devtoolset-2/root/usr/lib/gcc/x86_64-redhat-linux/4.8.2/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-E' '-v' '-shared-libgcc' '-mtune=generic' '-march=x86-64' 

clang++ configuration:

john@hurricane /home/john/repo/phoenix [PHX-29|✚5] $ clang++ -E -x c++ - -v < /dev/null clang version 3.6.0 (trunk 222833) (llvm/trunk 222832) Target: x86_64-unknown-linux-gnu Thread model: posix Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.4.4 Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.4.7 Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.4.7 Candidate multilib: .;@m64 Candidate multilib: 32;@m32 Selected multilib: .;@m64 "/usr/local/bin/clang" -cc1 -triple x86_64-unknown-linux-gnu -E -disable-free -disable-llvm-verifier -main-file-name - -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -target-linker-version 2.23.52.0.1 -v -dwarf-column-info -resource-dir /usr/local/bin/../lib/clang/3.6.0 -internal-isystem /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7 -internal-isystem /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/x86_64-redhat-linux -internal-isystem /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/backward -internal-isystem /usr/local/include -internal-isystem /usr/local/bin/../lib/clang/3.6.0/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir /home/john/repo/phoenix -ferror-limit 19 -fmessage-length 271 -mstackrealign -fobjc-runtime=gcc -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o - -x c++ - clang -cc1 version 3.6.0 based upon LLVM 3.6.0svn default target x86_64-unknown-linux-gnu ignoring nonexistent directory "/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7 /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/x86_64-redhat-linux /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/backward /usr/local/include /usr/local/bin/../lib/clang/3.6.0/include /usr/include End of search list. # 1 "<stdin>" # 1 "<built-in>" 1 # 1 "<built-in>" 3 # 320 "<built-in>" 3 # 1 "<command line>" 1 # 1 "<built-in>" 2 # 1 "<stdin>" 2 john@hurricane /home/john/repo/phoenix [PHX-29|✚5] $ 

I'm sure this can be fixed by passing the right parameters to clang's configure.sh, but I'm not sure what to pass?