cmd/go: change Package.Shlib to be the absolute path of the shared library

Makes little difference internally but makes go list output more useful.

Change-Id: I1fa1f839107de08818427382b2aef8dc4d765b36
Reviewed-on: https://go-review.googlesource.com/10192Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/cmd/go/build.go

@@ -782,8 +782,8 @@ func (b *builder) action1(mode buildMode, depMode buildMode, p *Package, looksha
 			b.actionCache[key] = a
 			return a
 		}
-		pkgs := readpkglist(filepath.Join(p.build.PkgTargetRoot, shlib))
-		a = b.libaction(shlib, pkgs, modeInstall, depMode)
+		pkgs := readpkglist(shlib)
+		a = b.libaction(filepath.Base(shlib), pkgs, modeInstall, depMode)
 		b.actionCache[key2] = a
 		b.actionCache[key] = a
 		return a

src/cmd/go/pkg.go

@@ -536,7 +536,8 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 			shlibnamefile := p.target[:len(p.target)-2] + ".shlibname"
 			shlib, err := ioutil.ReadFile(shlibnamefile)
 			if err == nil {
-				p.Shlib = strings.TrimSpace(string(shlib))
+				libname := strings.TrimSpace(string(shlib))
+				p.Shlib = filepath.Join(p.build.PkgTargetRoot, libname)
 			} else if !os.IsNotExist(err) {
 				fatalf("unexpected error reading %s: %v", shlibnamefile, err)
 			}