[msan] Add the FreeBSD AArch64 memory layout

[andrew]

Summary

Use the FreeBSD AArch64 memory layout values when building for it.
These are based on the x86_64 values, scaled to take into account the
larger address space on AArch64.

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

 //===- MemorySanitizer.cpp - detector of uninitialized reads --------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //

 // aarch64 Linux
 static const MemoryMapParams Linux_AArch64_MemoryMapParams = {
   0,               // AndMask (not used)
   0x06000000000,   // XorMask
   0,               // ShadowBase (not used)
   0x01000000000,   // OriginBase
 };
 
+// aarch64 FreeBSD
+static const MemoryMapParams FreeBSD_AArch64_MemoryMapParams = {
+  0x1800000000000,  // AndMask
+  0x0400000000000,  // XorMask
+  0x0200000000000,  // ShadowBase
+  0x0700000000000,  // OriginBase
+};
+
 // i386 FreeBSD
 static const MemoryMapParams FreeBSD_I386_MemoryMapParams = {
   0x000180000000,  // AndMask
   0x000040000000,  // XorMask
   0x000020000000,  // ShadowBase
   0x000700000000,  // OriginBase
 };
 
static const PlatformMemoryMapParams Linux_S390_MemoryMapParams = {
     &Linux_S390X_MemoryMapParams,
 };
 
 static const PlatformMemoryMapParams Linux_ARM_MemoryMapParams = {
   nullptr,
   &Linux_AArch64_MemoryMapParams,
 };
 
+static const PlatformMemoryMapParams FreeBSD_ARM_MemoryMapParams = {
+  nullptr,
+  &FreeBSD_AArch64_MemoryMapParams,
+};
+
 static const PlatformMemoryMapParams FreeBSD_X86_MemoryMapParams = {
   &FreeBSD_I386_MemoryMapParams,
   &FreeBSD_X86_64_MemoryMapParams,
 };
 
 static const PlatformMemoryMapParams NetBSD_X86_MemoryMapParams = {
   nullptr,
   &NetBSD_X86_64_MemoryMapParams,
if (ShadowPassed || OriginPassed) {
     CustomMapParams.ShadowBase = ClShadowBase;
     CustomMapParams.OriginBase = ClOriginBase;
     MapParams = &CustomMapParams;
   } else {
     Triple TargetTriple(M.getTargetTriple());
     switch (TargetTriple.getOS()) {
       case Triple::FreeBSD:
         switch (TargetTriple.getArch()) {
+          case Triple::aarch64:
+            MapParams = FreeBSD_ARM_MemoryMapParams.bits64;
+            break;
           case Triple::x86_64:
             MapParams = FreeBSD_X86_MemoryMapParams.bits64;
             break;
           case Triple::x86:
             MapParams = FreeBSD_X86_MemoryMapParams.bits32;
             break;
           default:
             report_fatal_error("unsupported architecture");