[safestack] Fix Mmap on FreeBSD AArch64

[andrew]

Summary

On FreeBSD AArch64 safestack needs to use __syscall to handle 64 bit arguments

[MaskRay]

I think placing the OS before && is more common.

compiler-rt/lib/safestack/safestack_platform.h

97

compiler-rt/lib/safestack/safestack_platform.h

 //===-- safestack_platform.h ----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
#else
   return syscall(SYS_tgkill, pid, tid, sig);
 #endif
 }
 
 inline void *Mmap(void *addr, size_t length, int prot, int flags, int fd,
                   off_t offset) {
 #if SANITIZER_NETBSD
   return __mmap(addr, length, prot, flags, fd, 0, offset);
-#elif defined(__x86_64__) && (SANITIZER_FREEBSD)
+#elif (defined(__aarch64__) || defined(__x86_64__)) && (SANITIZER_FREEBSD)
   return (void *)__syscall(SYS_mmap, addr, length, prot, flags, fd, offset);
 #else
   return (void *)syscall(SYS_mmap, addr, length, prot, flags, fd, offset);
 #endif
 }
 
 inline int Munmap(void *addr, size_t length) {
 #if SANITIZER_NETBSD