Discovered by poudriere: devel/linux-c7-devtools | linux-c7-devtools-7.8.2003_3: Failed: checksum make makesum solves the issue for me, leading to a successful build.
I filed the bug, its been about 8 months, the present linux-c7-devtools-7.9.2009 has no such issue, the fetch is fine.. this is no longer a bug.