Just to make sure you have tested the following: 1) standard GCC bootstrap (on any target) with and without the --with-zstd? 2) a cross compile with and without --with-zstd option? 3) a candian cross with and without --with-zstd option? including the auto option; actually how does pkg-config work in this case?
I am mostly worried about 3 here because that auto might use the wrong library and things go down hill from there. -- https://forge.sourceware.org/gcc/gcc/pulls/248#issuecomment-7817
