Revert "Remove -Alinker-messages"

This reverts commit e947492.
We need to allow linker messages so that they aren't caught by cargo's
`build.warnings = deny`.

Author: jyn514

src/bootstrap/src/core/builder/cargo.rs

@@ -344,6 +344,10 @@ impl Cargo {
             self.rustflags.arg("-Clink-arg=-gz");
         }
 
+        // Ignore linker warnings for now. These are complicated to fix and don't affect the build.
+        // FIXME: we should really investigate these...
+        self.rustflags.arg("-Alinker-messages");
+
         // Throughout the build Cargo can execute a number of build scripts
         // compiling C/C++ code and we need to pass compilers, archivers, flags, etc
         // obtained previously to those build scripts.