Why are we building gcc from scratch in the CI if I may ask?

[Raimo33]

I've noticed that our CI pipeline is compiling GCC from source, including internal files likeinsn-emit-6.cc and libraries such as libdecnumber and libbacktrace. This seems unusual for a typical CI workflow, which usually just builds and tests the project itself.

Could someone clarify why we are building GCC from scratch in the CI? Is it to ensure a consistent compiler version, to test patches against the compiler, or for some other reason?

[real-or-random]

Blaming will point you to 1deecaa, which GitHub shows to be included in #1313.