GH-44448: [C++] Add support for overwriting grpc_cpp_plugin path for cross-compiling

[kou]

Rationale for this change

We can't use find_package(gRPC) and gRPC::grpc_cpp_plugin for cross-compiling because it's for host. We need grpc_cpp_plugin for target in cross-compiling.

What changes are included in this PR?

Add ARROW_GRPC_CPP_PLUGIN CMake option that overwrites gRPC::grpc_cpp_plugin path found by find_package(gRPC).

Are these changes tested?

Yes.

conda-forge/arrow-cpp-feedstock#1432

Are there any user-facing changes?

Yes.

• GitHub Issue: [C++] cross-compilation issues with 18.0.0rc0: inclusion of <nmmintrin.h> resp. mis-detection of grpc_cpp_plugin #44448

[github-actions]

⚠️ GitHub issue #44448 has been automatically assigned in GitHub to PR creator.

[h-vetinari]

Thanks a lot for the quick PR!

It would be really nice if we could also change this where it's invoked, i.e.

arrow/cpp/src/arrow/flight/CMakeLists.txt

Lines 95 to 98 in 5ea3aa1

	COMMAND ${FLIGHT_PROTOC_COMMAND}
	"--grpc_out=${CMAKE_CURRENT_BINARY_DIR}"
	"--plugin=protoc-gen-grpc=$<TARGET_FILE:gRPC::grpc_cpp_plugin>"
	"${FLIGHT_PROTO}")

Currently our builds scripts are doing

sed -ie "s;protoc-gen-grpc.*$;protoc-gen-grpc=${BUILD_PREFIX}/bin/grpc_cpp_plugin\";g" ../src/arrow/flight/CMakeLists.txt

to work around this...

[kou]

This will work for the case because this overwrites $<TARGET_FILE:gRPC::grpc_cpp_plugin>.

[h-vetinari]

Confirmed in conda-forge/arrow-cpp-feedstock#1432 that this works, even without the sed command 🥳

[kou]

Thanks for confirming this. I'll merge this.