Tier 2 std support must always be known

Tier 2 std support must always be known · rust-lang/rust@34e6ea1

Original file line number	Diff line number	Diff line change
@@ -118,7 +118,7 @@ The `std` column in the table below has the following meanings:
`118`	`118`
`119`	`119`	`* ✓ indicates the full standard library is available.`
`120`	`120`	* \* indicates the target only supports [`no_std`] development.
`121`		`-* ? indicates the standard library support is unknown or a work-in-progress.`
	`121`	`+* ? indicates the standard library support is a work-in-progress.`
`122`	`122`
`123`	`123`	[`no_std`]: https://rust-embedded.github.io/book/intro/no-std.html
`124`	`124`