+ No functional change here, just renames and #include changes.
+ CMake can't have slashes in the target names. I'm suspciious of
that weird machinery for test, but I made it work.
+ A couple of builtins did not include their own headers, that
is no longer the case.
Prior to this change, builtins would take their arguments as `wchar_t **`.
This implies that the order of the arguments may be changed (which is
true, `wgetopter` does so) but also that the strings themselves may be
changed, which no builtin should do.
Switch them all to take `const wchar_t **` instead: now the arguments may
be rearranged but their contents may no longer be modified.
Now that the IWYU cleanup has been merged compile all, not just a couple, of
the builtin modules independent of builtin.cpp. That is, no longer `#include
builtin_NAME.cpp` in builtin.cpp. This is more consistent, more in line with
what developers expect, and is likely to reduce mistakes.
Reduces lint errors from 384 to 336 (-13%). Line count from 6307 to 4988 (-21%).
Another step in resolving issue #2902.
