cmd/go: look for __go_buildinfo section when looking for Mach-O version

This mirrors the ELF fix in CL 188957. TestScript/version failed on
darwin after that change.

Fixes #31861

Change-Id: I4ce953ebec8dd5fa47e26d373c59d7e290b75a34
Reviewed-on: https://go-review.googlesource.com/c/go/+/189159
Run-TryBot: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/internal/version/exe.go

@@ -213,7 +213,13 @@ func (x *machoExe) ReadData(addr, size uint64) ([]byte, error) {
 }
 
 func (x *machoExe) DataStart() uint64 {
-	// Assume data is first non-empty writable segment.
+	// Look for section named "__go_buildinfo".
+	for _, sec := range x.f.Sections {
+		if sec.Name == "__go_buildinfo" {
+			return sec.Addr
+		}
+	}
+	// Try the first non-empty writable segment.
 	const RW = 3
 	for _, load := range x.f.Loads {
 		seg, ok := load.(*macho.Segment)