Wt (the latest git version) now supports clang++.

This required remarkably little changes to Wt itself, a few bug fixes in llvm/clang with were quickly resolved with the excellent help from the clang++ team, and one workaround remaining for issue #6920. You will need the latest svn version of llvm and clang.

Initial profiling (using valgrind --tool=callgrind) also indicates that clang++ -O2 seems to optimize a bit better than g++ -O2. Not too shabby for such a young compiler !