x86/rounding-error test: add a bit of slack

Author: RalfJung

tests/pass/shims/x86/rounding-error.rs

@@ -26,8 +26,10 @@ fn main() {
                 let rel_error = (r - exact) / exact;
                 let log_error = rel_error.abs().log2();
                 assert!(
-                    rel_error == 0.0 || log_error < -12.0,
-                    "got an error of {rel_error} = 2^{log_error}"
+                    // Add a bit of slack since our log_error compuation gets rounded itself.
+                    rel_error == 0.0 || log_error < -12.0 + 1e-5,
+                    "correct result: {exact}, got: {r}\n\
+                    that's an error of {rel_error} = 2^{log_error}"
                 );
             }
         }