Coverage test for allowing coverage in a #![no_core] crate

tests/coverage/no-core.cov-map

@@ -0,0 +1,9 @@
+Function name: no_core::main
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 0c, 01, 00, 0d]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Counter(0)) at (prev + 12, 1) to (start + 0, 13)
+Highest counter ID seen: c0
+

tests/coverage/no-core.coverage

@@ -0,0 +1,13 @@
+   LL|       |#![feature(no_core)]
+   LL|       |#![no_core]
+   LL|       |//@ edition: 2021
+   LL|       |
+   LL|       |// Test that coverage instrumentation works for `#![no_core]` crates.
+   LL|       |
+   LL|       |// For this test, we pull in std anyway, to avoid having to set up our own
+   LL|       |// no-core or no-std environment. What's important is that the compiler allows
+   LL|       |// coverage for a crate with the `#![no_core]` annotation.
+   LL|       |extern crate std;
+   LL|       |
+   LL|      1|fn main() {}
+

tests/coverage/no-core.rs

@@ -0,0 +1,12 @@
+#![feature(no_core)]
+#![no_core]
+//@ edition: 2021
+
+// Test that coverage instrumentation works for `#![no_core]` crates.
+
+// For this test, we pull in std anyway, to avoid having to set up our own
+// no-core or no-std environment. What's important is that the compiler allows
+// coverage for a crate with the `#![no_core]` annotation.
+extern crate std;
+
+fn main() {}