cmake: don't export grpc_cpp_plugin when crosscompiling (#26148)

* cmake: don't install plugins when crosscompiling

Plugins should not be installed for a cross-compilation environment,
because it has to run on a host/build system. If it's installed then
configure stage fails with an error, that imported target references
non-existing file. Even if the file is found, it can't be used on a host.

Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>

* better way of detecting protoc targets

Co-authored-by: Jan Tattermusch <jtattermusch@google.com>

CMakeLists.txt

@@ -3722,7 +3722,7 @@ foreach(_hdr
 endforeach()
 
 
-if(gRPC_INSTALL)
+if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   install(TARGETS grpc_plugin_support EXPORT gRPCTargets
     RUNTIME DESTINATION ${gRPC_INSTALL_BINDIR}
     LIBRARY DESTINATION ${gRPC_INSTALL_LIBDIR}
@@ -10843,7 +10843,7 @@ target_link_libraries(grpc_cpp_plugin
 
 
 
-if(gRPC_INSTALL)
+if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   install(TARGETS grpc_cpp_plugin EXPORT gRPCTargets
     RUNTIME DESTINATION ${gRPC_INSTALL_BINDIR}
     LIBRARY DESTINATION ${gRPC_INSTALL_LIBDIR}
@@ -10882,7 +10882,7 @@ target_link_libraries(grpc_csharp_plugin
 
 
 
-if(gRPC_INSTALL)
+if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   install(TARGETS grpc_csharp_plugin EXPORT gRPCTargets
     RUNTIME DESTINATION ${gRPC_INSTALL_BINDIR}
     LIBRARY DESTINATION ${gRPC_INSTALL_LIBDIR}
@@ -10921,7 +10921,7 @@ target_link_libraries(grpc_node_plugin
 
 
 
-if(gRPC_INSTALL)
+if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   install(TARGETS grpc_node_plugin EXPORT gRPCTargets
     RUNTIME DESTINATION ${gRPC_INSTALL_BINDIR}
     LIBRARY DESTINATION ${gRPC_INSTALL_LIBDIR}
@@ -10960,7 +10960,7 @@ target_link_libraries(grpc_objective_c_plugin
 
 
 
-if(gRPC_INSTALL)
+if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   install(TARGETS grpc_objective_c_plugin EXPORT gRPCTargets
     RUNTIME DESTINATION ${gRPC_INSTALL_BINDIR}
     LIBRARY DESTINATION ${gRPC_INSTALL_LIBDIR}
@@ -10999,7 +10999,7 @@ target_link_libraries(grpc_php_plugin
 
 
 
-if(gRPC_INSTALL)
+if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   install(TARGETS grpc_php_plugin EXPORT gRPCTargets
     RUNTIME DESTINATION ${gRPC_INSTALL_BINDIR}
     LIBRARY DESTINATION ${gRPC_INSTALL_LIBDIR}
@@ -11038,7 +11038,7 @@ target_link_libraries(grpc_python_plugin
 
 
 
-if(gRPC_INSTALL)
+if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   install(TARGETS grpc_python_plugin EXPORT gRPCTargets
     RUNTIME DESTINATION ${gRPC_INSTALL_BINDIR}
     LIBRARY DESTINATION ${gRPC_INSTALL_LIBDIR}
@@ -11077,7 +11077,7 @@ target_link_libraries(grpc_ruby_plugin
 
 
 
-if(gRPC_INSTALL)
+if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   install(TARGETS grpc_ruby_plugin EXPORT gRPCTargets
     RUNTIME DESTINATION ${gRPC_INSTALL_BINDIR}
     LIBRARY DESTINATION ${gRPC_INSTALL_LIBDIR}

templates/CMakeLists.txt.template

@@ -689,6 +689,8 @@
   # grpcpp_channelz doesn't build with protobuf-lite, so no install required
   # See https://github.com/grpc/grpc/issues/22826
   if(gRPC_INSTALL AND NOT gRPC_USE_PROTO_LITE)
+  % elif tgt.build == 'protoc':
+  if(gRPC_INSTALL AND NOT CMAKE_CROSSCOMPILING)
   % else:
   if(gRPC_INSTALL)
   % endif