Rollup merge of #112300 - Zalathar:run-coverage, r=wesleywiser

Convert `run-make/coverage-reports` tests to use a custom compiletest mode

I was frustrated by the fact that most of the coverage tests are glued together with makefiles and shell scripts, so I tried my hand at converting most of them over to a newly-implemented `run-coverage` mode/suite in compiletest.

This ~~*mostly*~~ resolves #85009, ~~though I've left a small number of the existing tests as-is because they would require more work to fix/support~~.

---

I had time to go back and add support for the more troublesome tests that I had initially skipped over, so this PR now manages to completely get rid of `run-make/coverage-reports`.

---

The patches are arranged as follows:

- Declare the new mode/suite in bootstrap
- Small changes to compiletest that will be used by the new mode
- Implement the new mode in compiletest
- Migrate most of the tests over
- Add more code to bootstrap and compiletest to support the remaining tests
- Migrate the remaining tests (with some temporary hacks to avoid re-blessing them)
- Remove the temporary hacks and re-bless the migrated tests
- Remove the unused remnants of `run-make/coverage-reports`

1 files changed, 39 insertions, 0 deletions

diff --git a/tests/run-coverage/dead_code.coverage b/tests/run-coverage/dead_code.coverage
new file mode 100644
index 00000000000..09ff14c6f27
--- /dev/null
+++ b/tests/run-coverage/dead_code.coverage
@@ -0,0 +1,39 @@
+    1|       |#![allow(unused_assignments, unused_variables)]
+    2|       |
+    3|      0|pub fn unused_pub_fn_not_in_library() {
+    4|      0|    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+    5|      0|    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+    6|      0|    // dependent conditions.
+    7|      0|    let is_true = std::env::args().len() == 1;
+    8|      0|
+    9|      0|    let mut countdown = 0;
+   10|      0|    if is_true {
+   11|      0|        countdown = 10;
+   12|      0|    }
+   13|      0|}
+   14|       |
+   15|      0|fn unused_fn() {
+   16|      0|    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+   17|      0|    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+   18|      0|    // dependent conditions.
+   19|      0|    let is_true = std::env::args().len() == 1;
+   20|      0|
+   21|      0|    let mut countdown = 0;
+   22|      0|    if is_true {
+   23|      0|        countdown = 10;
+   24|      0|    }
+   25|      0|}
+   26|       |
+   27|      1|fn main() {
+   28|      1|    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+   29|      1|    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+   30|      1|    // dependent conditions.
+   31|      1|    let is_true = std::env::args().len() == 1;
+   32|      1|
+   33|      1|    let mut countdown = 0;
+   34|      1|    if is_true {
+   35|      1|        countdown = 10;
+   36|      1|    }
+                   ^0
+   37|      1|}
+