Rollup merge of #93479 - smoelius:master, r=yaahc

Use `optflag` for `--report-time`

Essentially, what is described here:
https://github.com/rust-lang/rust/issues/64888#issuecomment-1008047228

There is one difference. The comment proposes to add a
`--report-time-color` option. This change instead uses libtest's
existing `--color` option for that purpose.

src/doc/rustc/src/tests/index.md

@@ -267,7 +267,7 @@ Controls the format of the output. Valid options:
 
 Writes the results of the tests to the given file.
 
-#### `--report-time` _FORMAT_
+#### `--report-time`
 
 ⚠️ 🚧 This option is [unstable](#unstable-options), and requires the `-Z
 unstable-options` flag. See [tracking issue

src/doc/unstable-book/src/compiler-flags/report-time.md

@@ -21,11 +21,8 @@ Sample usage command:
 Available options:
 
 ```sh
---report-time [plain|colored]
-                Show execution time of each test. Available values:
-                plain = do not colorize the execution time (default);
-                colored = colorize output according to the `color`
-                parameter value;
+--report-time
+                Show execution time of each test.
                 Threshold values for colorized output can be
                 configured via
                 `RUST_TEST_TIME_UNIT`, `RUST_TEST_TIME_INTEGRATION`