cmd/go: added missing space to pkg-config errors

pkg-config errors were missing a space between pkg-config flags and packages
e.g.  pkg-config --cflags --staticsdl2

Fixes #25260

Change-Id: Iacecb697c5782c4822db9eefa1a2e4c4daf91a69
GitHub-Last-Rev: 2adf8576be66e31160c109a79f3853feac293f1b
GitHub-Pull-Request: golang/go#25261
Reviewed-on: https://go-review.googlesource.com/111638
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/internal/work/exec.go

@@ -987,7 +987,7 @@ func (b *Builder) getPkgConfigFlags(p *load.Package) (cflags, ldflags []string,
 		var out []byte
 		out, err = b.runOut(p.Dir, nil, b.PkgconfigCmd(), "--cflags", pcflags, "--", pkgs)
 		if err != nil {
-			b.showOutput(nil, p.Dir, b.PkgconfigCmd()+" --cflags "+strings.Join(pcflags, " ")+strings.Join(pkgs, " "), string(out))
+			b.showOutput(nil, p.Dir, b.PkgconfigCmd()+" --cflags "+strings.Join(pcflags, " ")+" -- "+strings.Join(pkgs, " "), string(out))
 			b.Print(err.Error() + "\n")
 			return nil, nil, errPrintedOutput
 		}
@@ -1002,7 +1002,7 @@ func (b *Builder) getPkgConfigFlags(p *load.Package) (cflags, ldflags []string,
 		}
 		out, err = b.runOut(p.Dir, nil, b.PkgconfigCmd(), "--libs", pcflags, "--", pkgs)
 		if err != nil {
-			b.showOutput(nil, p.Dir, b.PkgconfigCmd()+" --libs "+strings.Join(pcflags, " ")+strings.Join(pkgs, " "), string(out))
+			b.showOutput(nil, p.Dir, b.PkgconfigCmd()+" --libs "+strings.Join(pcflags, " ")+" -- "+strings.Join(pkgs, " "), string(out))
 			b.Print(err.Error() + "\n")
 			return nil, nil, errPrintedOutput
 		}