cmd/link: duplicate symbol reference pow on Windows

[emidoots]

What does 'go version' print?
go version devel +ff82d3107ab3 Sun Aug 31 22:49:14 2014 -0400 windows/amd64

What steps reproduce the problem?

Create a program that uses math.h / pow function in two separate packages. Try to link
them together into one main program:

1. bug/bug.go: http://play.golang.org/p/nFkVRN6qN-
2. bug/one/one.go: http://play.golang.org/p/4e68AXsW1r
3. bug/two/two.go: http://play.golang.org/p/f3pNq-xniD
4. go install bug

What happened?
# bug
C:\Users\stephen\Desktop\godev\pkg\windows_amd64/bug/two.a(_all.o): duplicate symbol
reference: pow in both bug/one(.text) and bug/two(.text)

What should have happened instead?
The package should link properly.

Please provide any additional information below.

This is a simplified example of a bug I ran into recently. I have an application that
imports a CGO wrapper to the Chipmunk 2D physics engine and a CGO wrapper to GLFW. The
program links fine on Linux -- but I cannot build it on windows due to this issue.

FWIW I am using (TDM) MinGW-W64 4.8.1 rev2

[emidoots]

Comment 1:

Possibly related to:
https://golang.org/issue/8702

[ianlancetaylor]

Comment 2:

Labels changed: added repo-main, release-go1.4, os-windows.

Status changed to Accepted.

[rsc]

Comment 3:

Issue #8702 has been merged into this issue.

[rsc]

Comment 4:

I'd love to fix this but it really requires having external linking support on Windows,
and that's not going to happen for 1.4.

Labels changed: added release-go1.5, removed release-go1.4.

[frederich]

I'm working on it.

[emidoots]

@frederich Can you clarify a bit? Working on getting 6l to accept it -- or working on external linking support on Windows?

[frederich]

@slimsag look at @rsc comment above "It really requires having external linking support". I think this should be the goal.

[steeve]

That would be great, thanks for doing it.
That would fix #9095