Remove warning from the embedded cmake step

[povik]

In some build environments (but not all) the following warning appears:

/tmp/yosys-slang > make
make build-slang
make[1]: Entering directory '/tmp/yosys-slang'
make configure-slang
make[2]: Entering directory '/tmp/yosys-slang'
cmake -S .//third_party/slang -B build/slang \
	-DCMAKE_INSTALL_PREFIX=build/slang_install \
	-DSLANG_INCLUDE_TESTS=OFF \
	-DSLANG_INCLUDE_TOOLS=OFF \
	-DCMAKE_BUILD_TYPE=Release \
	-DSLANG_USE_MIMALLOC=OFF \
	-DCMAKE_CXX_FLAGS="-fPIC" \
	-DCMAKE_DISABLE_FIND_PACKAGE_Boost=ON \
	-DCMAKE_DISABLE_FIND_PACKAGE_fmt=ON
-- CMake version: 3.22.1
-- slang version: 6.0.0+713164b8
-- The CXX compiler identification is GNU 11.4.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found Python: /usr/bin/python3.10 (found version "3.10.12") found components: Interpreter
-- Build STATIC library as: svlang
-- {fmt} version: 11.0.2
-- Build type: Release
-- Using remote fmt library
-- Using vendored boost_unordered header
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY - Success
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY - Success
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR - Success
-- Configuring done
-- Generating done
CMake Warning:
  Manually-specified variables were not used by the project:

    CMAKE_DISABLE_FIND_PACKAGE_fmt


-- Build files have been written to: /tmp/yosys-slang/build/slang

Reported by @hpretl in #43.

This ticket is to either understand why it shows up, or to address it.

[akashlevy]

What happens if you remove -DCMAKE_DISABLE_FIND_PACKAGE_fmt=ON from the Makefile on the affected platforms? Is this define even needed?

I'm not seeing any issues either with or without this flag on CentOS 7 (x64) and macOS (arm64)

[povik]

Is this define even needed?

The define is there to prevent cmake from picking up the system version of fmt for slang, otherwise the plugin gets improperly linked. Ideally we would adapt to either case in the plugin's Makefile but we need to find a clean solution for that.