Minor update:
Somewhere between rL201729 and RELEASE_350/final, the fix was changed to:
#if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L                                                                                                                                                                                      
#if !defined(__CLANG_MAX_ALIGN_T_DEFINED) || __has_feature(modules)                                                                                                                                                                            
#ifndef _MSC_VER                                                                                                                                                                                                                               
typedef struct {                                                                                                                                                                                                                               
  long long __clang_max_align_nonce1                                                                                                                                                                                                           
      __attribute__((__aligned__(__alignof__(long long))));                                                                                                                                                                                    
  long double __clang_max_align_nonce2                                                                                                                                                                                                         
      __attribute__((__aligned__(__alignof__(long double))));                                                                                                                                                                                  
} max_align_t;                                                                                                                                                                                                                                 
#else                                                                                                                                                                                                                                          
typedef double max_align_t;                                                                                                                                                                                                                    
#endif                                                                                                                                                                                                                                         
#define __CLANG_MAX_ALIGN_T_DEFINED                                                                                                                                                                                                            
#endif                                                                                                                                                                                                                                         
#endif