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

$ go version
go version go1.12 linux/amd64

Does this issue reproduce with the latest release?

Yes, but it does not happen with go 1.11.5

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

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/remy/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/remy/travail/go:/storage/remy/gopath"
GOPROXY=""
GORACE=""
GOROOT="/usr/lib/go"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build301410002=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Create a 2-file package which invokes a C function with untyped constants.

% cat a.go
package pkg

import "fmt"
import "math"

/*
#include 

typedef struct {
	uint64_t a;
	uint64_t b;
	void *next;
} T;

uint64_t mul(T *x, uint64_t mod, uint32_t unused) {
	return (x->a * x->b);
}
*/
import "C"

func F() {
	t := &C.T{a: 1, b: 2, next: nil}

	n := C.mul(t, math.MaxUint64, 1)
	fmt.Println(n)
}

func G() {
	t := &C.T{a: 1, b: 2, next: nil}

	n := C.mul(t, 1<<64-1, z)
	fmt.Println(n)
}

% cat b.go
package pkg

const (
	x = 1 << iota
	y
	z
)

What did you expect to see?

Successful compilation (as with go1.11.5)

What did you see instead?

./a.go:24:94: cannot use _cgo1 (type int) as type _Ctype_ulong in argument to _Cfunc_mul
./a.go:24:22: constant 18446744073709551615 overflows int
./a.go:31:70: cannot use _cgo2 (type int) as type _Ctype_uint in argument to _Cfunc_mul

The error disappears if MaxUint64 is defined in the same package, or if z is defined in the same file.