What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.
1. "go install -x test" with http://play.golang.org/p/LrE1XbZQxu
2. Notice that -lblah *is not* on the gcc command.

3. "go install -x test" with http://play.golang.org/p/noe6YfG2AO
4. Notice that -lblah *is* on the gcc command and that you get the (correct) error.

What is the expected output?
You should receive the following error compiling both programs:

# test
/usr/bin/ld: cannot find -lblah
collect2: ld returned 1 exit status

What do you see instead?
You do not get the above error. Even though the CGO docs at:

http://golang.org/cmd/cgo/

Specifically say you can use pseudo #cgo directives prefixed by "$GOOS, $GOARCH, or
$GOOS/$GOARCH", but $GOOS/$GOARCH does not actually get matched at all.

Which compiler are you using (5g, 6g, 8g, gccgo)?
6g

Which operating system are you using?
linux/amd64

Which version are you using?  (run 'go version')
tip

go version devel +62e67a664a03 Fri Sep 20 17:27:56 2013 -0700 linux/amd64

Please provide any additional information below.
It seems cgo does not support OR operators in the form of $GOOS/$GOARCH like it says in
the docs. AND operators are supported using spaces, for example:

#cgo windows amd64 LDFLAGS: -lblah

works on any windows or amd64 platform. But OR operators do not work:

#cgo linux/amd64 LDFLAGS: -lblah

Does not match on any platform at all (even linux/amd64).