[clang] Fix the warning for a non-void consteval function without a return...

[clang] Fix the warning for a non-void consteval function without a return value to actually say "consteval".

This warning was modified in 796ed03b to use the term "consteval"
for consteval functions. However the warning has never worked as
intended since the diagnostic's arguments are used in the wrong order.

This was unfortunately missed by 796ed03b since no test did exercise
this specific warning.

Additionally send the NamedDecl* into the diagnostic instead of just the
IdentifierInfo* to correctly work with special names and template
arguments.