hsc2hs is instructed compile C++ headers with GCC

When interfacing with C++ with hsc2hs, you usually want to compile the headers with g++, not with gcc.
Cabal always passes `--cc=/usr/bin/gcc` to hsc2hs so it's not possible to specify, that the headers should be built with g++. This makes, using hsc2hs on C++ headers, very hard.
Interfacing with C++ code without hsc2hs, seems to choose the right compiler automatically, maybe some similar mechanism could be used for hsc2hs?