library check target fails with apple clang 9

[reuk]

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