What does "redeclared with a different identifier" error in the gcc compiler mean when there is only one defintion

I have an arm project that I am building with the gcc compiler. I get an error(s) from the manufacturers libraries:

 carm E289: ["C:\yada\yada\Include\core_cmInstr.h" 388/57] "__NOP" redeclared with a different type
 carm E387: ["C:\yada\yada\Include\core_cmInstr.h" 388/57] "__NOP" redeclared with different function qualifiers

So I figure that the symbol __NOP is being declared twice in my project somewhere, but upon further inspection, the only place it is defined in the project is in the core_cmInstr.h file. So I'm having a hard time wrapping my head around the problem. These are the two places where the symbol __NOP is defined:

#define __NOP                             __nop

__attribute__( ( always_inline ) ) __STATIC_INLINE void __NOP(void)
{
  __ASM volatile ("nop");
}

Any ideas on what the error could mean?