* don't unconditionally pass -lz3 for mingw builds. If mingw builds
require this then the llvm-config executable should put it as part of
--system-libs. If there is a bug and it does not do that, and we need
a workaround, then the workaround should be an explicit cmake option.
* don't link libstage2.a against -lntdll. This causes zig to set
`builtin.link_mode == .Dynamic` and include the TLS definitions,
which then collide with the mingw-w64 symbols. This should probably
be addressed separately, but for now this solves the problem and
there is no reason to link a static library against a DLL.
* Findllvm.cmake no longer treats the libraries as "optional" and will
emit a cmake error if one is not found. Additionally, the
not-required LLVM library LLVMTableGen is omitted.
15ab61b2a0