[BOLT] Robustify compile-time config check

[urnathan]

Summary

When working on the BOLT runtime config stuff, I noticed its common.h header file is a little lax in checking its own config. As we're hard coding system call numbers, let's be a little more paranoid. So,

*) Verify x86_64
*) Use linux to enable linux bits
*) Use APPLE to enable apple bits
*) #error when these are not available

IMHO This makes it very clear this is for a specific pair of systems.

[rafauler]

LGTM

bolt/runtime/common.h

 //===- bolt/runtime/common.h ------------------------------------*- C++ -*-===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
-#if !defined(__APPLE__)
+#if !defined(__x86_64__)
+#error "For x86_64 only"
+#endif
+
+#if defined(__linux__)
 
 #include <cstddef>
 #include <cstdint>
 
 #include "config.h"
 
 #ifdef HAVE_ELF_H
 #include <elf.h>
 #endif
 
-#else
+#elif defined(__APPLE__)
 
 typedef __SIZE_TYPE__ size_t;
 #define __SSIZE_TYPE__                                                         \
   __typeof__(_Generic((__SIZE_TYPE__)0, unsigned long long int                 \
                       : (long long int)0, unsigned long int                    \
                       : (long int)0, unsigned int                              \
                       : (int)0, unsigned short                                 \
                       : (short)0, unsigned char                                \
                       : (signed char)0))
 typedef __SSIZE_TYPE__ ssize_t;
 
 typedef unsigned long long uint64_t;
 typedef unsigned uint32_t;
 typedef unsigned char uint8_t;
 
 typedef long long int64_t;
 typedef int int32_t;
 
+#else
+#error "For Linux or MacOS only"
 #endif
 
 // Save all registers while keeping 16B stack alignment
 #define SAVE_ALL                                                               \
   "push %%rax\n"                                                               \
   "push %%rbx\n"                                                               \
   "push %%rcx\n"                                                               \
   "push %%rdx\n"                                                               \