Auto merge of #129156 - Oneirical:final-curtest-call, r=<try>

run-make: Delete `cat-and-grep-sanity-check` and restrict `branch-protection-check-IBT` to stable

Part of #121876 and the associated [Google Summer of Code project](https://blog.rust-lang.org/2024/05/01/gsoc-2024-selected-projects.html).

First, this PR deletes the now useless `cat-and-grep-sanity-check` test.

Second, it revisits the `branch-protection-check-IBT` test, which was disabled due to a nonsensical `llvm_components` check. #126720 states that the test does work on stable rustc, so let's check this: added `//@ only-stable`.

If this works, some of the FIXME and commented-out lines will need cleanup before merging.

Please try:

try-job: x86_64-gnu-stable

tests/run-make/branch-protection-check-IBT/_rmake.rs → tests/run-make/branch-protection-check-IBT/rmake.rs

@@ -4,17 +4,16 @@
 // python3 x.py test --target x86_64-unknown-linux-gnu  tests/run-make/branch-protection-check-IBT/
 
 //@ only-x86_64
+//@ only-stable
 
-//@ ignore-test
 // FIXME(jieyouxu): see the FIXME in the Makefile
 
-use run_make_support::{cwd, env_var, llvm_readobj, rustc};
+use run_make_support::{cwd, llvm_components_contain, llvm_readobj, rustc};
 
 fn main() {
-    let llvm_components = env_var("LLVM_COMPONENTS");
-    if !format!(" {llvm_components} ").contains(" x86 ") {
-        return;
-    }
+    // if !llvm_components_contain("x86") {
+    //     panic!();
+    // }
 
     rustc()
         .input("main.rs")