Windows: Use local configuration for LLVM when linking dynamically

[HertzDevil]

Similar to how openssl_VERSION is already used on Windows, LLVM will now locate the first file called llvm_VERSION from CRYSTAL_LIBRARY_PATH, reading its contents to configure LLVM, rather than running %LLVM_CONFIG%. This file should consist of 3 lines:

• the output of llvm-config --version, using the same llvm-config.exe that built LLVM-C.dll
• the output of llvm-config --targets-built
• the output of llvm-config --system-libs (we assume --libs --ldflags do nothing more than locating LLVM-C.lib in the original LLVM installation)

On my LLVM 18-dev build, the file looks like this:

18.0.0git
X86
psapi.lib shell32.lib ole32.lib uuid.lib advapi32.lib

Then to make dynamic linking work, copy lib/LLVM-C.lib from LLVM to the Crystal installation's lib/llvm-dynamic.lib, as well as bin/LLVM-C.dll to the Crystal compiler's directory. This means we will be able to distribute LLVM as a dynamic-only library on Windows, without having to also distribute llvm-config.exe at all, since the above configuration is essentially synchronized to the DLL provided by Crystal.

This PR does not touch our Windows CI, that will be the next step.