[Bug c++/70452] [5/6 Regression] Regression in C++ parsing performance between 4.9.3 and 5.3.1

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70452

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hashtable lookups are from location/block remapping done.  I _think_ that if
all the copy_body stuff we do for constexpr evaluation would just "drop"
locations for the copy we'd still be fine constexpr wise but would save
quite a lot of linemap overhead and compile-time (hash-table lookup for
combined locs via set_block for example).

So maybe add a new field to copy_body_data for this purpose.