Programming Tools Guide
Chapter 3, C language compiler
Keywords

Keywords

The following identifiers are reserved for use as keywords and may not be used otherwise: 

 asm        default   for        short     union
 auto       do        goto       signed    unsigned
 break      double    if         sizeof    void
 case       else      int        static    volatile
 char       enum      long       struct    while
 const      extern    register   switch
 continue   float     return     typedef
The keyword asm is reserved in all compilation modes except -Xc. The keyword __asm is a synonym for asm and is available under all compilation modes, although a warning issued when it is used under the -Xc mode.

NOTE: Under the -Xm mode, the keywords: 
 cdecl   near   far   huge
are reserved but ignored. cdecl is silently ignored; the other three will cause a warning to be issued.

Under the -Xk mode, the following are considered identifiers and are not reserved as keywords: 

 const   signed   volatile