Missing float128 builtins on x86-64


I’m trying to use a clang built from source to compile some code that uses float128s and that targets x86-64. However, when I do so the linker complains it’s missing symbols like __trunctfdf2 and __extenddftf2. These symbols seem to be missing from compiler-rt library archive for x86-64. Is there a way to build the compiler-rt to have them included in the archive? Or is the assumption that these symbols should come from somewhere else on x86-64? If so, where are they supposed to come from?