Handling GCC __mode__

I have to run a Clang tool against code that compiles against an RTOS. Deep in the bowels of the RTOS std::uint64_t is eventually typedefed as such:

typedef unsigned int _GCC_ATTR_ALIGN_u64t attribute((mode(DI)));

unsigned int is a 32-bit value, but _GCC_ATTR_ALIGN_u64t is a 64-bit value. After quite a bit of searching I learned that the mode attribute is what is causing it to be 64-bits.

Does Clang support mode or is there some other way for me to make it so that Clang see _GCC_ATTR_ALIGN_u64t as 64-bits?