This requires setting CMAKE_CXX_COMPILER_TARGET manually; the LLVM
build system infers the wrong architecture when CMake is an
x86_64 binary.
(The wrong inferred architecture doesn't affect building libcxx,
but the wrong architecture gets passed as --target= parameter
when running the tests.)
Since 9c67ae861ccb0312fc680414a8441892d169d14a in llvm-project
(May 9th), these tests should pass on aarch64 too.
Co-authored-by: Jeremy Drake <github@jdrake.com>
