[clang] Track function template instantiation from definition (#112241)

This fixes instantiation of definition for friend function templates,
when the declaration found and the one containing the definition have
different template contexts.

In these cases, the the function declaration corresponding to the
definition is not available; it may not even be instantiated at all.

So this patch adds a bit which tracks which function template
declaration was instantiated from the member template. It's used to find
which primary template serves as a context for the purpose of
obtainining the template arguments needed to instantiate the definition.

Fixes #55509

Relanding patch, with no changes, after it was reverted due to revert of
commit this patch depended on.

0 files changed, 0 insertions, 0 deletions