[PATCH] contrib/persistent-https: update ldflags syntax for Go 1.7+

From: Parker Moore <redacted>

This fixes contrib/persistent-https builds for Go v1.7+ and is
compatible with Go v1.0+.

Running `make all` in `contrib/persistent-https` results in a failure
on Go 1.7 and above.

Specifically, the error is:

    go build -o git-remote-persistent-https \
   -ldflags "-X main._BUILD_EMBED_LABEL 1468613136"
    # _/Users/parkr/github/git/contrib/persistent-https
    /usr/local/Cellar/go/1.7rc1/libexec/pkg/tool/darwin_amd64/link: -X
flag requires argument of the form importpath.name=value
    make: *** [git-remote-persistent-https] Error 2

This `name=value` syntax for the -X flag was introduced in Go v1.5
(released Aug 19, 2015):

- release notes: https://golang.org/doc/go1.5#link
- commit: https://github.com/golang/go/commit/12795c02f3d6fc54ece09a86e70aaa40a94d5131

In Go v1.7, support for the old syntax was removed:

- release notes: https://tip.golang.org/doc/go1.7#compiler
- commit: https://github.com/golang/go/commit/51b624e6a29b135ce0fadb22b678acf4998ff16f

This patch includes the `=` to fix builds with Go v1.7+.

Thanks-to: Junio C Hamano [off-list ref]
Signed-off-by: Parker Moore <redacted>
---
 contrib/persistent-https/Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/contrib/persistent-https/Makefile

b/contrib/persistent-https/Makefile
index 92baa3be..2b4173d 100644

--- a/contrib/persistent-https/Makefile
+++ b/contrib/persistent-https/Makefile

@@ -25,8 +25,10 @@ git-remote-persistent-http: git-remote-persistent-https
        ln -f -s git-remote-persistent-https git-remote-persistent-http

 git-remote-persistent-https:
+       case $$(go version) in \
+               "go version go"1.[0-5].*) EQ=" " ;; *) EQ="=" ;; esac && \
        go build -o git-remote-persistent-https \
-               -ldflags "-X main._BUILD_EMBED_LABEL $(BUILD_LABEL)"
+               -ldflags "-X main._BUILD_EMBED_LABEL$${EQ}$(BUILD_LABEL)"

 clean:
        rm -f git-remote-persistent-http* *.tar.gz