Compile fail on clang 3.3

Compiling pioneer with clang 3.3, on arch linux, x86_64:

<pre>
make[2]: Entering directory `.../pioneer/src/collider'
clang++ -DPACKAGE_NAME=\"pioneer\" -DPACKAGE_TARNAME=\"pioneer\" -DPACKAGE_VERSION=\"0.00\" -DPACKAGE_STRING=\"pioneer\ 0.00\" -DPACKAGE_BUGREPORT=\"pioneer-dev@pioneerspacesim.net\" -DPACKAGE_URL=\"\" -DPACKAGE=\"pioneer\" -DVERSION=\"0.00\" -I. -I./.. -isystem ../../contrib -DPIONEER_VERSION=\"git\" -DPIONEER_EXTRAVERSION=\"acecd8a\" -DGLEW_STATIC   -I/usr/include/freetype2  -I/usr/include/libdrm  -DLUA_USE_POSIX -D_REENTRANT -I/usr/include/SDL2  -I/usr/include/sigc++-2.0 -I/usr/lib/sigc++-2.0/include    -I/usr/include -std=gnu++11 -Wall -Wformat -Wstrict-aliasing=2 -Wmissing-format-attribute -Wmissing-noreturn -Wdisabled-optimization -Wfloat-equal -Wshadow -Wcast-qual -Wcast-align -Wformat-security -Wold-style-cast -Wsign-promo -g -O2 -O3 -MT BVHTree.o -MD -MP -MF .deps/BVHTree.Tpo -c -o BVHTree.o BVHTree.cpp
clang++ -DPACKAGE_NAME=\"pioneer\" -DPACKAGE_TARNAME=\"pioneer\" -DPACKAGE_VERSION=\"0.00\" -DPACKAGE_STRING=\"pioneer\ 0.00\" -DPACKAGE_BUGREPORT=\"pioneer-dev@pioneerspacesim.net\" -DPACKAGE_URL=\"\" -DPACKAGE=\"pioneer\" -DVERSION=\"0.00\" -I. -I./.. -isystem ../../contrib -DPIONEER_VERSION=\"git\" -DPIONEER_EXTRAVERSION=\"acecd8a\" -DGLEW_STATIC   -I/usr/include/freetype2  -I/usr/include/libdrm  -DLUA_USE_POSIX -D_REENTRANT -I/usr/include/SDL2  -I/usr/include/sigc++-2.0 -I/usr/lib/sigc++-2.0/include    -I/usr/include -std=gnu++11 -Wall -Wformat -Wstrict-aliasing=2 -Wmissing-format-attribute -Wmissing-noreturn -Wdisabled-optimization -Wfloat-equal -Wshadow -Wcast-qual -Wcast-align -Wformat-security -Wold-style-cast -Wsign-promo -g -O2 -O3 -MT CollisionSpace.o -MD -MP -MF .deps/CollisionSpace.Tpo -c -o CollisionSpace.o CollisionSpace.cpp
In file included from BVHTree.cpp:4:
In file included from ./BVHTree.h:8:
In file included from /usr/lib64/gcc/x86_64-unknown-linux-gnu/4.8.1/../../../../include/c++/4.8.1/vector:60:
In file included from /usr/lib64/gcc/x86_64-unknown-linux-gnu/4.8.1/../../../../include/c++/4.8.1/bits/stl_algobase.h:64:
In file included from /usr/lib64/gcc/x86_64-unknown-linux-gnu/4.8.1/../../../../include/c++/4.8.1/bits/stl_pair.h:59:
In file included from /usr/lib64/gcc/x86_64-unknown-linux-gnu/4.8.1/../../../../include/c++/4.8.1/bits/move.h:57:
/usr/lib64/gcc/x86_64-unknown-linux-gnu/4.8.1/../../../../include/c++/4.8.1/type_traits:269:39: error: use of undeclared identifier '__float128'
    struct __is_floating_point_helper<__float128>
                                      ^
</pre>

The error is caused by clang using gcc headers from /usr/lib/gcc which is caused by the flag --std=gnu++11 defined in configure.ac. Changing the flag to --std=c++11 fixes the issue.