add test for issue 85155 and similar

This test reproduces post-monomorphization errors one can encounter
when using incorrect immediate arguments to some of the stdarch
intrinsics using const generics.

src/test/ui/consts/const-eval/auxiliary/post_monomorphization_error.rs

@@ -0,0 +1,20 @@
+// Auxiliary crate used for testing post-monomorphization errors cross-crate.
+// It duplicates the setup used in `stdarch` to validate its intrinsics' const arguments.
+
+struct ValidateConstImm<const IMM: i32, const MIN: i32, const MAX: i32>;
+impl<const IMM: i32, const MIN: i32, const MAX: i32> ValidateConstImm<IMM, MIN, MAX> {
+    pub(crate) const VALID: () = {
+        let _ = 1 / ((IMM >= MIN && IMM <= MAX) as usize);
+    };
+}
+
+macro_rules! static_assert_imm1 {
+    ($imm:ident) => {
+        let _ = $crate::ValidateConstImm::<$imm, 0, { (1 << 1) - 1 }>::VALID;
+    };
+}
+
+// This function triggers an error whenever the const argument does not fit in 1-bit.
+pub fn stdarch_intrinsic<const IMM1: i32>() {
+    static_assert_imm1!(IMM1);
+}

src/test/ui/consts/const-eval/issue-85155.rs

@@ -0,0 +1,21 @@
+// This is a test with a setup similar to issue 85155, which triggers a const eval error: a const
+// argument value is outside the range expected by the `stdarch` intrinsic.
+//
+// It's not the exact code mentioned in that issue because it depends both on `stdarch` intrinsics
+// only available on x64, and internal implementation details of `stdarch`. But mostly because these
+// are not important to trigger the diagnostics issue: it's specifically about the lack of context
+// in the diagnostics of post-monomorphization errors (PMEs) for consts, happening in a dependency.
+// Therefore, its setup is reproduced with an aux crate, which will similarly trigger a PME
+// depending on the const argument value, like the `stdarch` intrinsics would.
+//
+// aux-build: post_monomorphization_error.rs
+// build-fail: this is a post-monomorphization error, it passes check runs and requires building
+//             to actually fail.
+
+extern crate post_monomorphization_error;
+
+fn main() {
+    // This function triggers a PME whenever the const argument does not fit in 1-bit.
+    post_monomorphization_error::stdarch_intrinsic::<2>();
+    //~^ NOTE the above error was encountered while instantiating
+}

src/test/ui/consts/const-eval/issue-85155.stderr

@@ -0,0 +1,15 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/auxiliary/post_monomorphization_error.rs:7:17
+   |
+LL |         let _ = 1 / ((IMM >= MIN && IMM <= MAX) as usize);
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attempt to divide `1_usize` by zero
+
+note: the above error was encountered while instantiating `fn stdarch_intrinsic::<2_i32>`
+  --> $DIR/issue-85155.rs:19:5
+   |
+LL |     post_monomorphization_error::stdarch_intrinsic::<2>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.