The reboot tests cannot be built on ppc64el which uses the gccgo compiler.
We see
FAIL github.com/juju/juju/api/reboot [build failed]
which is confirmed by this output earlier in the unittest log
# testmain
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o): In function `github_com_juju_juju_api_reboot.ClearReboot.pN37_github_com_juju_juju_api_reboot.State':
/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:67: multiple definition of `github_com_juju_juju_api_reboot.ClearReboot.pN37_github_com_juju_juju_api_reboot.State'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:67: first defined here
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o): In function `github_com_juju_juju_api_reboot.GetRebootAction.pN37_github_com_juju_juju_api_reboot.State':
/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:90: multiple definition of `github_com_juju_juju_api_reboot.GetRebootAction.pN37_github_com_juju_juju_api_reboot.State'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:90: first defined here
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o): In function `github_com_juju_juju_api_reboot.RequestReboot.pN37_github_com_juju_juju_api_reboot.State':
/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:45: multiple definition of `github_com_juju_juju_api_reboot.RequestReboot.pN37_github_com_juju_juju_api_reboot.State'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:45: first defined here
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o): In function `github_com_juju_juju_api_reboot.WatchForRebootEvent.pN37_github_com_juju_juju_api_reboot.State':
/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:30: multiple definition of `github_com_juju_juju_api_reboot.WatchForRebootEvent.pN37_github_com_juju_juju_api_reboot.State'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:30: first defined here
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o):(.data.rel.ro.__go_tdn_github_com_juju_juju_api_reboot.State+0x0): multiple definition of `__go_tdn_github_com_juju_juju_api_reboot.State'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):(.data.rel.ro.__go_tdn_github_com_juju_juju_api_reboot.State+0x0): first defined here
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o): In function `github_com_juju_juju_api_reboot.State$hash':
/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/export_test.go:12: multiple definition of `github_com_juju_juju_api_reboot.State$hash'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:109: first defined here
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o): In function `github_com_juju_juju_api_reboot.State$equal':
/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/export_test.go:12: multiple definition of `github_com_juju_juju_api_reboot.State$equal'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:109: first defined here
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o):(.rodata.github_com_juju_juju_api_reboot.NewState$descriptor+0x0): multiple definition of `github_com_juju_juju_api_reboot.NewState$descriptor'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):(.rodata.github_com_juju_juju_api_reboot.NewState$descriptor+0x0): first defined here
/tmp/go-build573700990/github.com/juju/juju/api/reboot/_test/github.com/juju/juju/api/libreboot.a(reboot.o): In function `github_com_juju_juju_api_reboot.NewState':
/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:20: multiple definition of `github_com_juju_juju_api_reboot.NewState'
/tmp/go-build573700990/github.com/juju/juju/api/libreboot.a(reboot.o):/home/ubuntu/juju-core_1.21-alpha2/src/github.com/juju/juju/api/reboot/reboot.go:20: first defined here
collect2: error: ld returned 1 exit status
I believe these tests were introduced in commit 6ffffa3
This is reminiscent of bug 1289067 but it's not clear why the reboot api addition triggered the failures. I can't reproduce the linker error on amd64 with gccgo.