valgrind: doesn't build with an old clang

[mojca (Mojca Miklavec)]

valgrind fails to build already at configure time if clang from xcode 425 is used, complaining about too old compiler:

checking for a supported version of gcc... no (applellvm-4.2)
configure: error: please use gcc >= 3.0 or clang >= 2.9 or icc >= 13.0

A naive addition to the Portfile that blacklisted /usr/bin/clang++ (and llvm-gcc-4.2 just in case) made the build succeed:

PortGroup           compiler_blacklist_versions 1.0
compiler.blacklist  *gcc* {clang < 500}

but I didn't test macports-clang-3.3, llvm-gcc-4.2 or xcode 5. I'm also not sure whether the port needs some special handling about gcc (I don't understand what the rest of the portfile does).

It is also possible that the configure script simply fails to realize that clang++ is in fact some flavour of clang 3.2 (based on LLVM 3.2svn) that might work if the configure check was fixed.

I can do more tests if needed.