In llvm#78436 we made some SourceLocExpr dependent to
deal with the fact that their value should reflect the name of
specialized function - rather than the rtemplate in which they
are first used.

However SourceLocExpr are unusual in two ways
 - They don't depend on template argumente
 - They morally depend on the context in which they are used
   (rather than called from).

It's fair to say that this is quite novels and confuses
clang. In particular, in some cases, we used to create
dependent SourceLocExpr and never subsequently transform them,
leaving dependent objects in instantiated functions types.
To work around that we avoid replacing SourceLocExpr when we think
they could remain dependent.
It's certainly not perfect but it fixes a number of reported bugs,
and seem to only affect scenarios in which the value of the
SourceLocExpr does not matter (overload resolution).

Fixes llvm#106428
Fixes llvm#81155

Co-authored-by: Aaron Ballman <aaron@aaronballman.com>