cmd/go: compile runtime/internal/syscall as a runtime package

runtime/internal/syscall is a runtime package, so it should be built
with -+.

Specifically, we don't want libfuzzer instrumentation in Go functions
defined in runtime/internal/syscall, which is disabled with -+.

For #53190.

Change-Id: I9f16f5c7c7ce10b98371e9de82fcea6da854e163
Reviewed-on: https://go-review.googlesource.com/c/go/+/413818
Run-TryBot: Michael Pratt <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: prattmic

src/cmd/go/internal/work/gc.go

@@ -30,15 +30,16 @@ import (
 const trimPathGoRootFinal string = "$GOROOT"
 
 var runtimePackages = map[string]struct{}{
-	"internal/abi":            struct{}{},
-	"internal/bytealg":        struct{}{},
-	"internal/cpu":            struct{}{},
-	"internal/goarch":         struct{}{},
-	"internal/goos":           struct{}{},
-	"runtime":                 struct{}{},
-	"runtime/internal/atomic": struct{}{},
-	"runtime/internal/math":   struct{}{},
-	"runtime/internal/sys":    struct{}{},
+	"internal/abi":             struct{}{},
+	"internal/bytealg":         struct{}{},
+	"internal/cpu":             struct{}{},
+	"internal/goarch":          struct{}{},
+	"internal/goos":            struct{}{},
+	"runtime":                  struct{}{},
+	"runtime/internal/atomic":  struct{}{},
+	"runtime/internal/math":    struct{}{},
+	"runtime/internal/sys":     struct{}{},
+	"runtime/internal/syscall": struct{}{},
 }
 
 // The Go toolchain.