cmd/go: include .syso files even if CGO_ENABLED=0

A .syso file may include information that should go into the object file
that is not object code, and should be included even if not using cgo.
The example in the issue is a Windows manifest file.

Fixes #16050.

Change-Id: I1f4f3f80bb007e84d153ca2d26e5919213ea4f8d
Reviewed-on: https://go-review.googlesource.com/24032
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/cmd/go/go_test.go

@@ -2898,3 +2898,25 @@ func TestBinaryOnlyPackages(t *testing.T) {
 	tg.run("run", tg.path("src/p3/p3.go"))
 	tg.grepStdout("hello from p1", "did not see message from p1")
 }
+
+// Issue 16050.
+func TestAlwaysLinkSysoFiles(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+	tg.tempDir("src/syso")
+	tg.tempFile("src/syso/a.syso", ``)
+	tg.tempFile("src/syso/b.go", `package syso`)
+	tg.setenv("GOPATH", tg.path("."))
+
+	// We should see the .syso file regardless of the setting of
+	// CGO_ENABLED.
+
+	tg.setenv("CGO_ENABLED", "1")
+	tg.run("list", "-f", "{{.SysoFiles}}", "syso")
+	tg.grepStdout("a.syso", "missing syso file with CGO_ENABLED=1")
+
+	tg.setenv("CGO_ENABLED", "0")
+	tg.run("list", "-f", "{{.SysoFiles}}", "syso")
+	tg.grepStdout("a.syso", "missing syso file with CGO_ENABLED=0")
+}

src/cmd/go/pkg.go

@@ -1022,9 +1022,10 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 		p.MFiles = nil
 		p.SwigFiles = nil
 		p.SwigCXXFiles = nil
-		p.SysoFiles = nil
 		// Note that SFiles are okay (they go to the Go assembler)
 		// and HFiles are okay (they might be used by the SFiles).
+		// Also Sysofiles are okay (they might not contain object
+		// code; see issue #16050).
 	}
 
 	// The gc toolchain only permits C source files with cgo.