What version of Go are you using (go version)?

$ go version
go version go1.14.1 windows/amd64                                                                                              

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

$ go env

What did you do?

Build an executable that uses a large C library statically linked.

What did you expect to see?

A smaller executable

What did you see instead?

A kind-of large executable.

I'm not completely sure about this, but when Go links, either statically or dynamically, I think it includes a reference to all C functions wrapped with CGO in the resulting executable, even if those functions are never called.
It would help to only include required C symbols. This could in theory help the C compiler do dead code ilimination with static libraries. Adding the CFLAGS -ffunction-sections -fdata-sections, and LDFLAGS -Wl,-gc-sections could also do something.
Thanks.