ledger fails to link at build time once OpenBSD removes syscall(2)

[jrick]

OpenBSD is removing the syscall(2) interface soon, and this will break ledger builds on the platform:

$ go install ./ledger     
# github.com/howeyc/ledger/ledger
/home/jrick/src/go/pkg/tool/openbsd_amd64/link: running clang failed: exit status 1
ld: error: undefined symbol: syscall
>>> referenced by zsyscall_openbsd_amd64.s:213 (/home/jrick/src/go/src/syscall/zsyscall_openbsd_amd64.s:213)
>>>               /tmp/go-link-4273625514/go.o:(syscall.libc_syscall_trampoline.abi0)
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Updating to the latest golang.org/x/sys module fixes the build.