[cmake] Add missing dependencies to objlib in add_llvm_executable.

[fhahn]

Summary

After f06abbb393800b0d466c88e283c06f75561c432c I have been seeing build
failures due to the obj.clang target missing a dependency on
tools/clang/clang-tablegen-targets.

This appears to be due to the fact that LLVM_COMMON_DEPENDS are not added
as dependencies to the object library.

This patch uses the same logic as llvm_add_library to register
dependencies for object libraries.

[beanz]

LGTM, one comment.

llvm/cmake/modules/AddLLVM.cmake

972

Unless I'm misunderstanding the behavior issues you're seeing here are a bug in our code not CMake. IIUC, the issue you're seeing is that since the objlib doesn't depend on the tablegen targets, it is likely failing to build or building out of order. That's clearly a bug in our code, not CMake.

I know that you copied that comment, but it doesn't seem relevant here, and I think it is describing a situation that isn't actually a bug in CMake.

[steven_wu]

LGTM

[fhahn]

llvm/cmake/modules/AddLLVM.cmake

972

Thanks, I agree that the comment here is a bit out of place. I've removed it in the committed version.

llvm/cmake/modules/AddLLVM.cmake

if (LLVM_LINK_LLVM_DYLIB AND NOT ARG_DISABLE_LLVM_LINK_LLVM_DYLIB)
     set(USE_SHARED USE_SHARED)
   endif()
 
   set(EXCLUDE_FROM_ALL OFF)
   set_output_directory(${name} BINARY_DIR ${LLVM_RUNTIME_OUTPUT_INTDIR} LIBRARY_DIR ${LLVM_LIBRARY_OUTPUT_INTDIR})
   llvm_config( ${name} ${USE_SHARED} ${LLVM_LINK_COMPONENTS} )
   if( LLVM_COMMON_DEPENDS )
     add_dependencies( ${name} ${LLVM_COMMON_DEPENDS} )
+    foreach(objlib ${obj_name})
+      add_dependencies(${objlib} ${LLVM_COMMON_DEPENDS})
+    endforeach()
   endif( LLVM_COMMON_DEPENDS )
 
   if(NOT ARG_IGNORE_EXTERNALIZE_DEBUGINFO)
     llvm_externalize_debuginfo(${name})
   endif()
   if (LLVM_PTHREAD_LIB)
     # libpthreads overrides some standard library symbols, so main
     # executable must be linked with it in order to provide consistent