Commit b1b5105ceb moved the following block
#ifdef AT_HWCAP2 if (getauxval( AT_HWCAP2 ) & 2) syscall_flags |= SYSCALL_HAVE_WRFSGSBASE; #endif
out of an #ifdef __linux__ block and it now causes failures on FreeBSD and others which do not have getauxval. Guard this invocation properly.