CMake-produced Xcode project fails to build

I checked out llvm, clang, and compiler-rt, then ran the following
command to generate an Xcode project:

% pwd
% mkdir CMakeRoot
% cd CMakeRoot
% cmake -G Xcode -DLLVM_TARGETS_TO_BUILD="X86" ../

I opened the resulting LLVM.xcodeproj and tried to build the ALL_BUILD
target. It failed while trying to build asan:

clang: error: invalid argument '-mmacosx-version-min=10.9' not allowed
with '-mios-simulator-version-min=7.0'
failed with exit code 1

Is this a known problem?

--Kyle Sluder