libgo patch committed: Pass CGO_LDFLAGS to linker for cgo

[Ian Lance Taylor]

This patch from Peter Collingbourne backports a patch from the master
repository to pass CGO_LDFLAGS to the linker when using cgo with
gccgo.  Bootstrapped and ran Go testsuite on x86_64-unknown-linux-gnu.
Committed to mainline.

Ian

diff -r b0a83aacb539 libgo/go/cmd/go/build.go
--- a/libgo/go/cmd/go/build.go  Fri Jan 09 13:17:25 2015 -0800
+++ b/libgo/go/cmd/go/build.go  Fri Jan 09 16:41:10 2015 -0800
@@ -1895,6 +1895,7 @@
        }
        ldflags = append(ldflags, afiles...)
        ldflags = append(ldflags, cgoldflags...)
+       ldflags = append(ldflags, envList("CGO_LDFLAGS", "")...)
        ldflags = append(ldflags, p.CgoLDFLAGS...)
        if usesCgo && goos == "linux" {
                ldflags = append(ldflags, "-Wl,-E")