internal/syscall/unix: use our own version of this package

The upstream one assumes it's running on a Unix system (which makes
sense), but this package is also used on baremetal. So replace it on
systems that need a replaced syscall package.

src/internal/syscall/unix/eaccess.go

@@ -0,0 +1,10 @@
+package unix
+
+import "syscall"
+
+func Eaccess(path string, mode uint32) error {
+	// We don't support this syscall on baremetal or wasm.
+	// Callers are generally able to deal with this since unix.Eaccess also
+	// isn't available on Android.
+	return syscall.ENOSYS
+}