Add comments to -Zlink-* tests

Author: ChrisDenton

tests/ui/link-native-libs/issue-70093/link-directives.rs

@@ -1,8 +1,13 @@
+// Ensure that `#[link]` attributes are entirely ignore when using `-Zlink-directives=no`.
+
 //@ run-pass
 //@ compile-flags: -Zlink-directives=no
 //@ ignore-fuchsia - missing __libc_start_main for some reason (#84733)
 //@ ignore-cross-compile - default-linker-libraries=yes doesn't play well with cross compiling
 
+// Usually these `#[link]` attribute would cause `libsome-random-non-existent-library`
+// to be passed to the linker, causing it to fail because the file doesn't exist.
+// However, with -Zlink-directives=no, the `#[link]` is ignored.
 #[link(name = "some-random-non-existent-library", kind = "static")]
 extern "C" {}
 

tests/ui/link-native-libs/issue-70093/link-native-libraries.rs

@@ -1,3 +1,6 @@
+// Ensure that rust does not pass native libraries to the linker when
+// `-Zlink-native-libraries=no` is used.
+
 //@ run-pass
 //@ compile-flags: -Zlink-native-libraries=no -Cdefault-linker-libraries=yes
 //@ ignore-fuchsia - missing __libc_start_main for some reason (#84733)
@@ -14,6 +17,9 @@
 //@[msvc] compile-flags: -Clink-arg=msvcrt.lib
 //@[msvc] only-msvc
 
+// Usually these `#[link]` attribute would cause `libsome-random-non-existent-library`
+// to be passed to the linker, causing it to fail because the file doesn't exist.
+// However, -Zlink-native-libraries=no disables that.
 #[link(name = "some-random-non-existent-library", kind = "static")]
 extern "C" {}