list(REMOVE_ITEM) should accept one argument
Given
set(omitted_targets one two three)
# Comment this to reproduce the failure
set(LLVM_TARGETS_TO_BUILD X86)
list(REMOVE_ITEM omitted_targets ${LLVM_TARGETS_TO_BUILD})
we get
$ cmake -P cmaketest.cmake
CMake Error at cmaketest.cmake:6 (list):
list sub-command REMOVE_ITEM requires two or more arguments.
Like target_*
commands, this subcommand could be tolerant of empty cmake variables.