[C++][CMake] handle Protobuf_PROTOC_EXECUTABLE correctly in cross-compilation

[h-vetinari]

Describe the bug, including details regarding any error messages, version, and platform.

In the preparation for releasing arrow v16 in conda-forge (where we need to cross-compile for various targets), @raulcd ended up raising #41333 which got fixed in #41360. However, as I was working on the backports, I noticed that there's a hunk missing here in apache/arrow compared to what got committed in conda-forge/arrow-cpp-feedstock@b80a399, namely

diff --git a/cpp/cmake_modules/FindProtobufAlt.cmake b/cpp/cmake_modules/FindProtobufAlt.cmake
index f343b42f2..98a3281ee 100644
--- a/cpp/cmake_modules/FindProtobufAlt.cmake
+++ b/cpp/cmake_modules/FindProtobufAlt.cmake
@@ -31,6 +31,12 @@ endif()
 find_package(protobuf CONFIG ${find_package_args})
 set(ProtobufAlt_FOUND ${protobuf_FOUND})
 if(ProtobufAlt_FOUND)
-  if(Protobuf_PROTOC_EXECUTABLE)
-    set_target_properties(protobuf::protoc PROPERTIES
-    IMPORTED_LOCATION_RELEASE "${Protobuf_PROTOC_EXECUTABLE}"
-  )
-  endif()
   set(ProtobufAlt_VERSION ${protobuf_VERSION})
   set(ProtobufAlt_VERSION_MAJOR ${protobuf_VERSION_MAJOR})
   set(ProtobufAlt_VERSION_MINOR ${protobuf_VERSION_MINOR})

Component(s)

C++, Packaging

[raulcd]

Issue resolved by pull request 41582
#41582