[Debuginfo] [CSInfo] Do not create CSInfo for undef arguments

If a function parameter is marked as "undef", prevent creation
of CallSiteInfo for that parameter.
Without this patch, the parameter's call_site_value would be incorrect.
The incorrect call_value case reported in PR39716,
addressed in D85111.
​
Patch by Nikola Tesic
​
Differential revision: https://reviews.llvm.org/D92471