fix(build) Look up `llvm-config.exe` and siblings

On Windows, the locate_llvm_config will look for llvm-config binary names as defined in LLVM_CONFIG_BINARY_NAMES, plus the same binary names with the .exe extension.

Indeed, when building LLVM 10, the LLVM build script generates a bin/llvm-config.exe binary file, not bin/llvm-config (which is also the case for all executables).