[clang] Reland: [clang] Track function template instantiation from definition (PR #125266)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

I’m not in a position where I can test the patch properly right now, but if the whole qtbase can be built (not only the reduced testcase or the specific source file that triggered the issue before), I’m good with it - thanks!

https://github.com/llvm/llvm-project/pull/125266