[compiler-rt][hwasan] Massage prctl/arch_prctl API constants.

[glider]

Summary

Move the definitions outside InitializeOsSupport(). Also remove the
undefs, as these constants won't be visible outside the .cpp file anyway.

compiler-rt/lib/hwasan/hwasan_linux.cpp

static uptr GetHighMemEnd() {
   return max_address;
 }
 
 static void InitializeShadowBaseAddress(uptr shadow_size_bytes) {
   __hwasan_shadow_memory_dynamic_address =
       FindDynamicShadowStart(shadow_size_bytes);
 }
 
-void InitializeOsSupport() {
 #  define PR_SET_TAGGED_ADDR_CTRL 55
 #  define PR_GET_TAGGED_ADDR_CTRL 56
 #  define PR_TAGGED_ADDR_ENABLE (1UL << 0)
 #  define ARCH_GET_UNTAG_MASK 0x4001
 #  define ARCH_ENABLE_TAGGED_ADDR 0x4002
+
+void InitializeOsSupport() {
   // Check we're running on a kernel that can use the tagged address ABI.
   int local_errno = 0;
   bool has_abi;
 #  if defined(__x86_64__)
   has_abi = (internal_iserror(internal_arch_prctl(ARCH_GET_UNTAG_MASK, 0),
                               &local_errno) &&
              local_errno == EINVAL);
 #  else
#  endif  // defined(__x86_64__) && !defined(HWASAN_ALIASING_MODE)
     if (flags()->fail_without_syscall_abi) {
       Printf(
           "FATAL: HWAddressSanitizer failed to enable tagged address syscall "
           "ABI.\nSuggest check `sysctl abi.tagged_addr_disabled` "
           "configuration.\n");
       Die();
     }
   }
-#  undef PR_SET_TAGGED_ADDR_CTRL
-#  undef PR_GET_TAGGED_ADDR_CTRL
-#  undef PR_TAGGED_ADDR_ENABLE
 }
 
 bool InitShadow() {
   // Define the entire memory range.
   kHighMemEnd = GetHighMemEnd();
 
   // Determine shadow memory base offset.
   InitializeShadowBaseAddress(MemToShadowSize(kHighMemEnd));