LLVM: Update to 18.1.4 * src/llvm.mk: Update version and checksum. It is no longer possible to build a shared libLLVM.dll for Windows in newer versions of LLVM because the maximum number of symbols that can be exported from a DLL is exceeded. Build static libraries instead. Set a windows-gnu target because the library naming scheme that llvm-config expects for windows-msvc (the default) is different. No changes for Linux build rule. * src/mesa.mk: Use static LLVM libraries when building for Windows.