Nobody should be merging pull requests here anyway, this is a read only mirror of the real repo. Changes need to be committed to the real repo, not here.
So squash the commits on the command line then push to the real repo from the command line. https://gcc.gnu.org/wiki/ForgeExperiment#Monitoring_and_merging_changes -- https://forge.sourceware.org/gcc/gcc-wwwdocs/pulls/3#issuecomment-7533
