Successfulyl bootsrapped llvm-gcc4 on mingw32

Hello, Everyone.

Today I've finished digging into llvm-gcc4 in order to build in under
mingw32. The most trickiest was to make libstdc++ build, since its
configure & makefiles are not so perfect as main gcc ones.

There are several problems with inline assemler (in two places at
least), but both of them are easily seen. Also, there are some
compiler crashes while compiling libiberty (with LLVM code-generator).

Now I'm making fresh build to clean up many small tweaks I've made.
The patches & bug reports will follow.