Ignore a test that uses thin LTO for cg_gcc

Author: bjorn3

tests/ui/lto/issue-105637.rs

@@ -11,6 +11,7 @@
 
 //@ aux-build: thinlto-dylib.rs
 //@ run-fail
+//@ ignore-backends: gcc
 //@ check-run-results
 
 extern crate thinlto_dylib;