[llvm] [GVN] Invalidate ICF cache when clearing the instructions (PR #68145)

[Wael Yehia via llvm-commits]

w2yehia wrote:

on AIX, we use libLTO.so (LTOCodegenerator) and it has the `-save-temps` option.
This option emits IR at intermediate steps of link-time LTO.
If you're using lld, you can pass `-save-temps` directly (i.e. without `-plugin-opt=`)
When I try it on ppclinux, I get these files for a simple hello world program:
```
a.out.0.0.preopt.bc  a.out.0.2.internalize.bc  a.out.0.4.opt.bc  a.out.0.5.precodegen.bc
```
Try a hello world testcase first, before applying it to the python link.

https://github.com/llvm/llvm-project/pull/68145