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

[Shivam Gupta via llvm-commits]

xgupta 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=`) 

Thanks. I get this working by using `-Wl,-plugin-opt=save-temps` so thought to add some documentation -
https://github.com/llvm/llvm-project/pull/68389.

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