I get an error running the library check target with apple clang 9: ``` Checking /Users/reuben/development/cbmc/src/ansi-c/library/intrin.c __libcheck.c:261:13: error: definition of builtin function '_mm_lfence' inline void _mm_lfence(void) ^ __libcheck.c:268:13: error: definition of builtin function '_mm_mfence' inline void _mm_mfence(void) ^ 2 errors generated. ``` `cc --version` gives the following: ``` Apple LLVM version 9.0.0 (clang-900.0.37) Target: x86_64-apple-darwin16.7.0 Thread model: posix InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin ```