Please answer these questions before submitting your issue. Thanks!

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

go version go1.9.4 linux/amd64

Does this issue reproduce with the latest release?

I don't know.

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/lion/go"
GORACE=""
GOROOT="/usr/lib/go"
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="/bin/gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build491035465=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

package main

/*
#include <stdio.h>
void do_something(_GoString_ go_string) {
    return;
}
*/
import "C"

func main() {
	C.do_something("example")
}

What did you expect to see?

Go compiles it successfully.

What did you see instead?

....go:12:2: could not determine kind of name for C.do_something

gcc errors for preamble:
....go:5:19: error: unknown type name '_GoString_'
 void do_something(_GoString_ go_string) {
                   ^~~~~~~~~~

Documentation

https://golang.org/cmd/cgo/#hdr-Go_references_to_C

A C function may be declared in the Go file with a parameter type of the special name _GoString_. This function may be called with an ordinary Go string value. The string length, and a pointer to the string contents, may be accessed by calling the C functions

size_t _GoStringLen(_GoString_ s);
const char *_GoStringPtr(_GoString_ s);

These functions are only available in the preamble, not in other C files. The C code must not modify the contents of the pointer returned by _GoStringPtr. Note that the string contents may not have a trailing NUL byte.