architecture dependent directory of C header

[Da Shi Cao]

When compiling a C source using gcc, the following list of directories to search for included header files could be displayed:
 /usr/lib/gcc/x86_64-linux-gnu/8/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/8/include-fixed
 /usr/include/x86_64-linux-gnu  <--- arch dependent?
 /usr/include

I'd like to know how this arch dependent directory (/usr/include/x86_64-linux-gnu) be incorporated into the gcc if a gcc compiler is to be built?

Thanks,
Dashi Cao