all: link to https instead of http

The one in misc/makerelease/makerelease.go is particularly bad and
probably warrants rotating our keys.

I didn't update old weekly notes, and reverted some changes involving
test code for now, since we're late in the Go 1.5 freeze. Otherwise,
the rest are all auto-generated changes, and all manually reviewed.

Change-Id: Ia2753576ab5d64826a167d259f48a2f50508792d
Reviewed-on: https://go-review.googlesource.com/12048
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/cgo/gcc.go

@@ -781,7 +781,7 @@ func (p *Package) gccCmd() []string {
 			// incorrectly typed unsigned long. We work around that
 			// by disabling the builtin functions (this is safe as
 			// it won't affect the actual compilation of the C code).
-			// See: http://golang.org/issue/6506.
+			// See: https://golang.org/issue/6506.
 			"-fno-builtin",
 		)
 	}