Porting to gcc 11 / intrinsics

[NightStrike via Gcc]

When porting to GCC 11, care must be taken to adjust includes of GCC
intrinsic headers due to this change:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97148

That should be reflected in:

https://gcc.gnu.org/gcc-11/porting_to.html