Use an explicit x86-64 cpu in tests that are sensitive to it

There are a few tests that depend on some target features **not** being
enabled by default, and usually they are correct with the default x86-64
target CPU. However, in downstream builds we have modified the default
to fit our distros -- `x86-64-v2` in RHEL 9 and `x86-64-v3` in RHEL 10
-- and the latter especially trips tests that expect not to have AVX.

These cases are few enough that we can just set them back explicitly.

tests/codegen/target-feature-inline-closure.rs

@@ -1,5 +1,5 @@
 //@ only-x86_64
-//@ compile-flags: -Copt-level=3
+//@ compile-flags: -Copt-level=3 -Ctarget-cpu=x86-64
 
 #![crate_type = "lib"]
 #![feature(target_feature_11)]