slang: the `slang` CLI binary is a tool target; SLANG_INCLUDE_TOOLS=OFF removes it

When building the slang SystemVerilog frontend from source just to get the command-line slang binary, don't pass -DSLANG_INCLUDE_TOOLS=OFF to save time. The driver is add_executable(slang_driver ...) in tools/driver/CMakeLists.txt, so with tools off, cmake --build build --target slang_driver fails with gmake: *** No rule to make target 'slang_driver', and --target help lists only the library (slang_slang). Configure with -DSLANG_INCLUDE_TOOLS=ON (tests can stay off) and build only --target slang_driver to keep the build small. Checked on slang master (2026-11).