Add CFLAGS_FOR_BUILD

Two patches to use this variable for Apple gcc/llvmgcc and
also set the variable in the configure command line env for
gcc/llvmgcc. An alternative to this part is to add it to
the build scripts and I may change to doing that later.
Pass binutil paths to gcc/llvmgcc configure

Add --with-{ld|ar|as|ranlib|lipo}=.. to the configure command lines
and remove the symlinks to these tools as they are found explicitly
now. The old the symlink method can't work on MSYS since ln is just
cp and readlink does not exist (so e.g. ar.exe couldn't locate
i686-apple-darwin11-ranlib.exe)
Two minor workarounds for Windows

1. Copy DLLs from lib to bin after building LLVM core.
2. rm -rf instead of rm -f on lib32 and lib64 as ln is cp.